A COURSE IN
EXPERIMENTAL PHYSIOLOGY
BY
GEORGE BACHMANN, M. D.
Professor of Physiology in the Emory University School of Medicine
Atlanta, Georgia
PRIVATELY PRINTED BY THE AUTHOR
Copyright 1918 by
G. Bachmann
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ELECTRICAL CONSIDERATIONS AND THE
GRAPHIC METHOD
GALVANIC ELECTRICITY.
The medical student has, presumably, a knowledge of electricity. For this reason the
following paragraphs will deal briefly with only the most fundamental facts and theories
of electricity as a preparation for an intelligent use of the electrical apparatus employed
in experimental physiology.
The Electric Cell.—This term is applied to an apparatus which generates electricity
by chemical action. In its simplest form an electric cell consists of two "elements"—a
zinc and a copper plate, or carbon, platinum, etc., instead of copper—immersed in an
"exciting fluid," commonly dilute sulphuric acid.
The sulphuric acid acts chemically upon the zinc plate with the result that zinc sul¬
phate is formed and hydrogen is liberated, in accordance with the following formula:
Zn+H2S04=ZnS04+H2
The atoms of the zinc go into solution as zinc ions bearing positive charges. The zinc
plate is consequently left negatively charged, just as when a glass rod is positively elec¬
trified by rubbing it with silk, the silk is left negatively charged. The solution about the
zinc plate becomes positively charged through the zinc ions. As the hydrogen ions have
likewise a positive charge, they are repelled by the positively charged zinc ions toward
the copper plate. When the repelled hydrogen ions reach the copper plate some of them
give up their charge of positive electricity to it and then collect as fine bubbles of hy¬
drogen gas. Thus the copper plate becomes positively charged.
When the zinc and copper plates are not connected, these phenomena continue for
only a short time, for the negative charge on the zinc plate soon becomes so great that it
attracts the positively charged zinc ions with as much force as the acid is pulling them
into solution. Similarly the copper plate soon accumulates a sufficiently large charge of
positive electricity to repel from itself the positively charged hydrogen ions with a force
equal to that exerted by the positively charged zinc ions in driving them out of solution.
Chemical action then ceases; but there exists now in the cell a definite difference of po¬
tential. The acid solution has the highest potential and is, therefore, positive both to the
zinc and the copper. The difference of potential between the acid solution and the cop¬
per is, however, not so great as between the solution and the zinc; the copper is, there¬
fore, at a higher potential than the zinc.
It follows that when the terminals ot' the plates are connected by a wire, a current
of electricity flows from the copper plate to the zinc plate and that their charges de¬
crease. The acid is, therefore, able once again to act upon the zinc which, passing in so¬
lution, drives the positively charged hydrogen ions to the copper plate as already ex¬
plained. These phenomena continue so long as the plates remain connected. There is
thus established a continuous flow, or current, of electricity which continues so long as
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there is any acid left in the solution and zinc to be acted upon. The flow of electricity
inside the cell is from zinc to copper, and outside the cell from copper to zinc. It is thus
seen that the electric current flows in a circle; hence, the pathway followed by the cur¬
rent is called a "circuit." This form of electric current is called a "continuous," or "gal¬
vanic," or "voltaic" current. Why?
The terminals of the plates are called the "poles" of the cell. Since the copper termi¬
nal is at a higher potential than the zinc terminal and gives a positive charge, it is called
the "positive" pole; for the reverse reasons the zinc terminal is called the "negative"
pole. When the two poles of the cell are connected by a "conductor," electricity leaves
(ascends from) the cell by the positive pole and returns( descends) to the cell by the
negative pole. For these reasons the poles are often called the "anode" and the "cath¬
ode" respectively.
A cell made as just described cannot maintain a current of constant strength for a
number of reasons:
(a) The sulphuric acid solution reacting chemically with the zinc, becomes gradually
changed into a solution of zinc sulphate; chemical action gradually diminishes and fi¬
nally ceases altogether. The electric current suffers the same fate.
(b) The bubbles of hydrogen which accumulate on the surface of the copper plate
prevent the free passage of electricity, gas being a bad conductor; when the hydrogen
bubbles have covered a considerable part of the surface of the copper plate, they vir¬
tually constitute a hydrogen plate. These two factors weaken the original current; the
first, by increasing the resistance to the passage of the current, the second, by changing one
of the materials of which the cell is made and therefore its potential difference. To this
phenomenon the term "polarization" of the cell is given.
Such a cell could not be used for physiological work in which a constant, uniform
strength of current is indispensable. There are, however, other cells in which these draw¬
backs have been eliminated. These cells are less violent in action, they are provided with
a means of preventing polarization and can maintain a current of uniform strength for
a long time. Among the cells most generally used in physiology may be mentioned: The
Daniell cell, the Grenet cell, and the ordinary dry cell. The latter, on account of its great
convenience, is now very largely employed. Another convenient source of electricity is the
storage battery.
The Dry Cell. —This consists, usually, of a zinc cup, coated inside with a layer of plas¬
ter of Paris saturated with ammonium chloride. A rod of carbon is placed in the center
of the cup. The space between the carbon rod and the plaster of Paris is filled with a mix¬
ture of charcoal and manganese dioxide. The upper part of the cell is sealed with pitch to
prevent evaporation. When the carbon and zinc plates are connected by a wire, a chem¬
ical action takes place between the ammonium chloride and the zinc with the result that
there is formed a double chloride of zinc and ammonium, and that hydrogen and ammonia
are liberated.
Zn-f4NH4Cl+2H20=ZnCl22NH;Cl+2NH4OH+H:
The hydrogen moves to the carbon plate where it tends to accumulate. For this rea¬
son a dry cell becomes rapidly polarized when used in a continuous manner for some little
time. When the cell is allowed to rest, it becomes depolarized through a union of the hy¬
drogen with the oxygen slowly given off by the manganese dioxide.
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The Storage Battery or Accumulator.—The ordinary storage battery consists of an
acid-proof vessel containing dilute sulphuric acid, into which are immersed two or more
lead plates. When the battery is discharged the acid acts upon the plates which are in
consequence, converted to a variable extent into lead sulphate. When an electric current
is passed through the battery, certain chemical changes occur in the plates. The plate by
which the current enters (the anode) is oxidized to lead oxide, in accordance with the
following equation:
PbS04+2H;0+S04=Pb02+4H+2S04
The plate by which the current leaves the battery (the kathode) is reduced to metal¬
lic lead, as follows:
PbS04+H2=Pb+2H+S04
When these changes have progressed sufficiently far, the battery is said to be
"charged." The charging current is then cut off.
After the battery has been charged the reverse chemical changes take place, and
when the plates are joined by a conductor, an electric current can be led off which remains
constant during the greater part of the battery's discharge. The metallic lead plate be¬
comes the anode, while the lead oxide plate becomes the kathode; the current continues
to flow until both plates are reconverted to lead sulphate. The battery is then complete¬
ly "discharged." Each desk in the laboratory can be supplied with an electric current
of a strength suitable for most experiments from a storage battery of appropriate size.
Electrical Units of Measurement.—In order to obtain and to be able to convey an
exact idea of electricity as a form of energy, it has been found necessary to devise means
whereby electricity and its effects can be estimated quantitatively. This has been accom¬
plished by the international adoption of certain definite standards of measurement of the
various electrical quantities. These standards of measurement represent the "units" of
the various quantities. Only those units which are of immediate practical importance in
physiology will be mentioned here.
It has been stated that there exists in an electric cell a difference of potential be¬
tween any two points of the entire circuit. The electricity must therefore move along
the circuit with a certain degree of force; this is termed the "electromotive force"—E.
M. F.—. The unit of measurement of the E. M. F. is called a "volt."
As the electricity flows along the circuit it meets with resistance. Of the total resist¬
ance some is found in that part of the circuit located within the cell; this is called the
"internal resistance" and is designated: r. The rest of the resistance is in that part of
the circuit outside the cell and is called the "external resistance" designated: R. The
resistance varies with the nature of the materials entering in the composition of the cell
and of the external part of the circuit. Furthermore the internal resistance varies directly
as the distance between the plates and inversely as their surface area. The external re¬
sistance varies inversely as the area of cross section of the conductor and directly as its
length. The unit employed in the measurement of resistance to electrical flow is called
the "ohm."
It is obvious that the electric current flowing along the circuit must have a certain
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intensity or strength. The current strength can be estimated by a unit of measurement
called the "ampere."*
The strength of the electric current will not depend entirely on the electromotive
force, but will be determined rather by the ratio existing between the E. M. F. and the
total resistance. This constitutes what is called: "Ohm's law," viz., that the strength of
a current will be directly proportional to the E. M. F- at that point and inversely propor¬
tional to the total resistance; or:
E. M. F.
C =
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When Ohm's law is applied to any portion of a circuit, it reads:
PD
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Where PD represents the potential difference between two points in the circuit, and
r the resistance of the conductor joining these two points.
When the units of measurement are substituted for the above signs, both equations
read:
Yolts
Amperes —
Ohms
What is the strength of an electric current when the E. M. F. of the cell —1.5 volts,
the internal resistance, r, = 5 ohms and the external resistance, R, = O? What is the
current strength when R = 250 ohms?
Batteries.—The tissues have a high resistance, and for this reason it is often neces¬
sary, in physiological and in medical work, to increase the strength of the current. This
can be done by uniting a number of cells, the collection of united cells being called a
"battery." There are several methods of arranging cells into batteries:
1. By joining the cells in "series." The positive pole of one cell is connected with
the negative pole of another cell, the positive pole of the latter is connected with the
negative pole of still another cell, and so on until the desired number of cells has been
connected. This method of uniting cells increases the E. M. F. in proportion to the num¬
ber of cells in the series, but it also increases in the same way the internal resistance; the
E. M. F. of the battery will therefore be that of the individual cell multiplied by the num¬
ber of cells in the battery, and the internal resistance that of the individual cell multi¬
plied by the number of cells in the battery.
♦The concrete standards of the practical international units are as follows:
"The international Ohm is the resistance offered to an unvarying electric current by a column
of mercury at the temperature of melting ice, 14.4521 grams in mass, of a constant cross-sectional
area and of the length of 106.3 centimeters.
"The international Ampere is the unvarying current which, when passed through a solution of
nitrate of silver in water, deposits silver at the rate of 0.001118 of a gram per second.
"The international Volt is the electromotive force that, steadily applied to a conductor whose
resistance is one international ohm, will produce a current of one international ampere."
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What will be the current strength of a battery of 6 cells (a) when the E. M. F. of one
cell = 1.5 volts: r = 5 ohms and R = 0?( (b) when R=250 ohms? What is a "milliam-
pere"?
2. By joining the cells in "parallel" or "multiple arc." The positive poles af all the
cells are connected with each other and the negative poles are similarly connected. The
effect of uniting cells in this way is equivalent to making a single cell with plates that
number of times larger than the individual plates as there are cells in the battery. The E.
M. F. will therefore remain the same as that of the single ordinary cell. The internal re¬
sistance will, however, be decreased in proportion to the number of cells in the battery.
Why?
What will be the current strength of a battery of 6 cells (a) when the E. M. F. of one
cell = 1.5 volts; r = 5 ohms and R = 0? (b) When R=250 ohms?
What method of uniting cells should be used, when the external resistance is high?
3. By joining the cells in "multiple series." This is a combination of the methods
just described. Separate groups of cells are joined in series; these groups are then joined
in multiple arc.
For example, three cells are joined in series and constitute one group; three such
groups are made and then joined in multiple arc. What will be the current strength of
this battery when the E. M. F. of one cell = 1.5 volts, r = 5 ohms, and R = 250 ohms?
Electrodes.—The wires which are used to conduct electricity, in physiological experi¬
ments, must always be insulated. The ends of the wires that are applied to the tissue un¬
der study, must, however, be clean and free from insulation. These ends are usually made
of platinum and are called "electrodes." For a few inches the wires are held in a rigid
holder, usually of vulcanite, which facilitates their handling.
When metallic electrodes, through which a current is continuously flowing, remain
in contact with the tissues for even a relatively short time, they become polarized. As this
polarization is undesirable, special electrodes have been devised which do not become po¬
larized, or do so in a negligible degree only. Such electrodes are called "non-polarizable
electrodes." They will be discussed later.
Keys.—Most tissues are good conductors of electricity. If therefore, the electrodes
are placed in contact with, say, a muscle, the electric current will flow from the end of
one wire to the end of the other wire across the intervening muscle substance. At the
time the wires are applied to the muscle the current is "made." If one, or both wires are
removed, the current is "broken." A current of electricity may, therefore, be made to
flow momentarily through part of an organ by bringing the ends of electrodes in contact
with the organ for the desired length of time. It is often more convenient, however, to
leave the electrodes in contact with the organ the entire time of an experiment and to
cause the current to flow or to be interrupted (by closing or opening the circuit) by
means of a mechanical device called a "key."
Keys are made in many different forms. Besides serving the purpose already mention¬
ed, namely: to close or open a circuit, keys are made which serve to divert a current
from the main circuit to a shorter circuit having a much smaller resistance. A key
serving this purpose is called a "short-circuiting key." Other keys have been devised
which serve to reverse the direction of the flow of a current. A key serving this purpose
is usually called a "commutator," "pole-changer," or "reverser."
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The Simple Key.—The simple key consists of an iron base, into which are fastened
two binding posts. These binding posts are insulated from the iron base by vulcanite
bushings. A copper bar with a vulcanite handle moves around a horizontal axis at the
end of one of the binding posts. A short distance from the handle is a platinum pin,
which comes in contact with a platinum plate on top of the other binding post when the
key is closed.
The contact between the pin and plate is maintained partly by the weight of the
copper bar, but mostly by a flat spring acting on the beveled end of the copper bar.
The circuit is "closed" and the current "made" when the copper bar is down. The
circuit is "open" and the current "broken" when the copper bar is raised.
The Short-Circuiting Key.—This consists of a base of slate on which are fastened trans¬
versely two strips of brass having a binding post at each end. In the middle of one
transverse strip is an upright provided with a horizontal pin around which moves a cop¬
per bar, the free end of which has a vulcanite handle. The bar, when lowered, engages be¬
tween two upright strips of spring brass, set in the middle of the other transverse strip.
The Commutator or Pole-Changer.—The best-known form of commutator is the one
devised by Pohl. The disadvantage of this instrument is that mercury must be used to ef¬
fect the contacts. This disadvantage has been overcome in other forms of commutators.
Of these, the most complete is one devised by Porter, who named the instrument a "rock-
ing-key." It can serve as a simple key, short-circuiting key, and pole-changer. The base
is of slate.
"The central binding posts are prolonged upwards and each is slotted to receive a
brass bar, which is pivoted in the slot by a horizontal pin. The brass bars are held paral¬
lel by two rubber rods which serve as handles. When the bars are depressed to one side
or the other, they engage between plates of spring brass set into brass blocks, each of
which carries a binding screw. Cross-wires enter these blocks, as shown in the figure. At
one end the cross-wires are soldered into the blocks, thus making an electrical contact.
The two blocks at the other end are perforated by rubber cores or "bushings" through
which the cross-wires pass. The cross-wires, therefore, make no electrical contact with
these blocks. When a contact is desired, the nut borne on the head of each cross-wire is
turned until its face presses against the brass block outside the bushing. In this position
the key serves as a pole-changer, or commutator. When the nut on the cross-bar between
the central posts is turned until its face presses against the post, it will short-circuit the
central posts." (Porter, W. T., An Introduction to Physiology, p. 50-51).
When all contact nuts are turned away from their respective posts, and the central
posts are connected with a source of electricity, the current can be led at will to either of
two pairs of electrodes in electrical connection with the end binding posts. The key acts
then as a "current-deflector."
EXPERIMENTS ILLUSTRATING THE USE OF THE KEYS.
A. The Simple Key.—Fasten wires to the poles of a cell, or to the binding posts of
any other source of electricity provided for experimental purposes, Connect one of the
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wires with a binding post of the simple key and a third wire with the other binding post
of the key. In all experiments the key must be kept open while connections are being
made.
Bring the ends of the wires together and complete the circuit by closing the key; a
current of continuous or galvanic electricity is flowing along the external part of the cir¬
cuit, from the positive to the negative pole of the source of supply.
The presence of this current can be readily shown by its effect, (1) on a magnetic needle,
(2) on the tongue.
The Effect of the Galvanic Current on a Magnetic Needle.—Place a small compass on
the table in such a way that the magnetic needle lies in the magnetic meridian (the needle
pointing north and south). Hold the ends of the wires in contact with each other, with
the thumb and forefinger of the left hand. Place the wire close to the glass cover of the
compass, parallel with the needle and in such a way that the current will flow from north
to south.
Make the current with the key. Is the needle deflected from its position of rest?
What direction does the north end take? Does the needle remain deflected so long as the
current is flowing? What happens on the break of the current?
Change the position of the wires so that the current will flow in the reverse direc¬
tion, viz., from south to north. Close and then open the key. What is the direction of de¬
flection of the north end?
Repeat these experiments with one wire under the compass and parallel with the
needle. Note the direction of deflection of the north end and compare the results with
those obtained when the current was made to flow above the needle.
Would the deflection of the needle be greater if the current were made to flow from
north to south above, and from south to north below instead of in one direction only?
what effect would a number of turns of the wire have on the extent of the deflection,
the current remaining the same?
What is (1) a galvanoscope, (2) a galvanometer?
The Effect of the Galvanic Current on the Tongue.—With the key open, place the
ends of the wires on the tongue. Make the circuit; let the current flow a few seconds,
then break the circuit.
What effect is produced (1) on the make, (2) on the break of the current? Which
effect is the stronger, the make or the break? Is there any sensation felt during the
continuous flow of the current?
B. The Short-Circuiting Key.--Connect one of the poles of the source of electricity
with one of the binding posts seen at the end of one of the transverse strips of the key.
Connect the other pole with the binding post of the other transverse strip on the same
side. Interpose a simple key along one of the wires. Fasten wires to the remaining two
binding posts of the short-circuiting key.
When the copper bar of the short-circuiting key is raised, the terminals of the wires
are in contact and the simple key is closed, the current flows along the entire (long) cir¬
cuit; when the bar of the short-circuiting key is lowered the current flows as far as the
•bar and returns to the source of electricity. The current is then said to be "short-circuit¬
ed." The short-circuiting of a current can be illustrated as follows:
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(a) Repeat the experiment with the magnetic needle in which the wire was placed
above and parallel with the needle, (1) with the short-circuiting key open, (2) with the
short-circuiting key closed.
(b) Repeat the experiment showing the effect of the galvanic current on the tongue,
(1) with the short-circuiting key open, (2) with the short-circuiting key closed.
Describe the results. Explain the effect of the short-circuiting key.
C. The Commutator or Pole-Changer,—(a) Used as a Current Reverser. Screw the
nuts at the ends of the cross-wires of the rocking key until they are in contact with the
brass blocks. Connect the source of electricity with the two binding posts of any one end
of the key, interposing a simple key along one of the wires. Fasten wires to the two bind¬
ing posts of the other end of the rocking key. See that the nut, on the cross bar between
the central posts, is not in contact with the post.
With the bars of the rocking key depressed to one side and the simple key open, hold
the terminals of the wire above the magnetic needle as in the previous experiments and
close the simple key. Note the deflection of the north end of the needle. Open the sim¬
ple key. Depress the bars of the rocking key to the other side. Close the simple key.
What is the direction of deflection of the north end of the needle? Open the simple key.
Explain the result and make a drawing showing the direction of the current in both posi¬
tions of the rocker.
(b) Used as a Current Deflector.—-Unscrew the contact nuts away from the brass
blocks iand connect the source of electricity with the central posts, the simple key being
interposed along one of the wires. Turn the nut on the cross bar (between the central
posts) away from the post. Connect hand electrodes to the binding posts at each end of
the key. piPP''
Place the platinum tips of the hand electrodes on the tongue, one pair on each side.
Depress the rocker to one side; close and open the simple key. Note on which side the shock
is felt. Depress the rocker to the other side; close and open the key. On which side
is the shock now felt? Explain the result and indicate on a diagram the course of the
current in each position of the rocker.
If a magnet is thrust into a coil of wire (or vice-versa), if a coil of wire is moved up
or down about a magnet, a current appears in the wire and continues so long as the move¬
ment lasts. The current is said to have been "induced" in the wire. This phenomenon,
discovered by Faraday, is the result of the "cutting" of the "lines of magnetic force"
which are found in the space about any magnet.
As any conductor, along which a current is flowing, is surrounded by lines of mag¬
netic force, such a conductor will behave like a magnet in inducing electricity in another
conductor placed in its proximity. The first conductor connected with the poles of a cell,
constitutes the "primary circuit"; the second conductor, Avhich need be nothing more than
a loop of wire, constitutes the "secondary circuit."
INDUCED ELECTRICITY.
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The production of electricity by induction, may be studied by placing a simple key
in the primary and a galvanometer in the secondary circuit; the circuits, should be placed
parallel to each other.
At the moment the key in the primary circuit is closed and the current is therefore
made, a current of short duration is induced in the secondary circuit as shown by the
deflection of the galvanometer needle and its immediate return to its position of rest. Dur¬
ing the continuous flow of the current along the primary circuit, there is no current in
the secondary circuit. At the moment the key is opened and the current in the primary
is therefore broken, another momentary current is induced in the secondary circuit as
shown by the movement of the galvanometer needle. In other words, the appearance
and the disappearance of a current in the primary circuit are both capable of inducing a
current in the secondary circuit.
If, while the current is flowing through the primary circuit, the circuits are either
approximated or separated, a current is induced in the secondary which lasts so long as
the movement of the circuits lasts.
Sudden changes in the strength of a current flowing steadily through the primary cir¬
cuit, either in the way of increase or of decrease, will also induce currents in the sec¬
ondary circuit.
The current in the primary circuit is called the "inducing" current; the current in the
secondary circuit is termed the "induced" current. Induced electricity is also named, in
honor of its discoverer, "faradic" electricity.
The induced current flows in a direction opposite to that of the inducing current,
(1) when the primary current is made, (2) when the circuits are approximated, (3) when
the strength of the primary current is suddenly increased. The induced current flows
in the same direction as the primary current under the reverse conditions.
The induced currents will be stronger if the circuits are arranged in the form of coils.
Other things being equal, the induced currents will be stronger the greater the number
of turns of wire in the secondary circuit in proportion to the number of turns in the pri¬
mary circuit. The induced currents can further be increased in strength by placing in
the primary coil a core of soft iron which, becoming magnetized when the current flows
through the primary, concentrates the force of the magnetic field.
The induced currents will be stronger the closer the coils are to each other, and con¬
versely, they will be weaker the greater the distance between the coils. Aside from the
factor of distance, the angular position of the coils in reference to each other, influences
the strength of the induced currents. When the secondary coil is at right angles to the
primary, no current can be induced in the secondary. The current in the secondary in¬
creases gradually as the angle diminishes and acquires its greatest strength when the two
coils are parallel to each other.
The induced current lasts but an instant and is of higher electromotive force than
the indncing current.
The Inductorium.—Based on the foregoing facts, an instrument has been devised for
ihe convenient production of induced electricity, to which the name "inductorium" has
been given.
Porter's inductorium consists of a primary coil of relatively stout insulated copper
11
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wire having a resistance of 0.5 ohms. This coil is supported by a strong vulcanite plate
into which three binding posts are secured. A bundle of shellacked, soft iron wire con¬
stitutes the core in the primary coil.
The secondary coil consists of 5,000 turns of fine, silk covered wire. Each layer of wire
is separated from its neighbor by a sheet of paraffined paper. The ends of the secondary
wire are fastened to two brass bars screwed to the sides of the vulcanite spool. Each
brass bar has in its center a trunnion capable of revolving in a brass block which is sol¬
dered to a short tube. These tubes slide upon side rods supported ,at one extremity by
the vulcanite plate already mentioned and at the other extremity by insulated brass feet.
The free extremity of the side rods is provided with binding posts. The induced currents
produced in the secondary coil are therefore led along these side rods to the binding posts
to which the wires of electrodes may be fastened. The secondary coil may be made to slide
on these rods until it completely surrounds the primary coil. The secondary coil can, fur¬
thermore, be rotated on its trunnions, in a vertical plane, to any angle in reference to the
axis of the primary coil. When the secondary coil has rotated through 90 deg., further
movement in that direction is prevented by means of a stop pin soldered to one of the
brass bars on the side of the secondary coil. The induced currents can be short-circuited
by closing the key seen back of the binding posts at the end of the side rods.
Single Induced Currents.—Connect one binding post of the source of electric supply
with one of the binding posts of the simple key. Run another wire from the other binding
post of the simple key to the left hand binding post of the inductorium. Connect the other
binding post of the source of supply with the middle binding post of the inductorium.
Keep the key open.
Attach the hand electrodes to the terminals of the secondary coil, viz., the binding
posts at the end of the side rods. Slide the secondary coil away from the primary as
far as it can go. Place the platinum tips of the electrodes against the tongue. Make,
and then break the primary current with the key. Was there any shock felt at the mak¬
ing or breaking of the current If not, gradually bring the secondary towards the pri¬
mary a half centimeter at a time, making aud breaking the primary current after each
advance of the secondary coil, until a distinct shock is felt.
Does this shock occur at the make or the break of the primary current? Continue
to slide the secondary toward the primary until shocks are felt at both the make and the
break. Which is the stronger of the two, the break or the make shock? What effect
on the strength of the induced current has the position of the secondary in reference to
the primary coil?
The induced current which occurs at the break of the primary current produces a
greater effect than the induced current which occurs at the make of the primary current.
This difference in the break and make effect is due to the development in the primary
coil, at the make of the current, of an "extra current" in each neighboring turn of the
wire. This phenomenon is termed "self-induction." The extra current which occurs at
the make, flows in a direction opposite to that of the battery current. For this reason,
the extra current prevents the primary current from attaining its maximum intensity as
rapidly as would otherwise be the case. Therefore, the magnetic field surrounding the pri¬
mary coil increases to its maximum strength very gradually and the lines of force pass slow¬
ly into the secondary coil. Consequently, the current induced in the secondary reaches its
12
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maximum development slowly. On the other hand, at the break of the primary current,
there is no retarding influence from the self-induced currents; hence the primary current
falls to zero in a very short time As its lines of force pass out of the secondary coil at a
much higher rate than they passed into it on the make of the primary, the E. M. F. in the sec¬
ondary 'rises to ia. higher level in a correspondingly shorter time. Since the effectiveness of
the electric current as a stimulus does not depend so much on its intensity as upon the
rapidity with which its intensity changes, the make induced current is not so powerful a
stimulus as the break induced current.
The Extra Current.—Remove the secondary coil from the inductorium. The connec¬
tions remaining the same as in the foregoing experiment, connect the tags of the hand
electrodes with the binding posts of the simple key to which the circuit wires are already
attached. Close the key. Place the platinum tips on the tongue; open the key.
Was a shock felt? Would the opening of a key produce this effect with a galvanic
current of the strength used? What explanation can be offered for the shock felt on the
opening of the key.
Replace the secondary coil.
Rapidly Repeated Induced Currents or '' Tetanizing'' Currents.—As a single induced
current lasts but a very short time, it is inadequate as a stimulus in all experiments where
prolonged stimulation is required. If, however, single induced currents follow each other
with sufficient rapidity, their effects will be summated and, in this way, stimulation can
be maintained for any desired length of time. Induced currents can be produced with
unvarying frequency by placing in the primary circuit an automatic interrupter which,
by vibrating, makes and breaks the primary current a definite number of times per
second.
The automatic interrupter consists essentially of an iron disc—or hammer—fastened to
the end of a spring. This spring is held in a collar which embraces the middle binding
post of the inductorium. About the middle of the spring is soldered a small plate of
platinum which comes in contact with the platinum tip of a set-screw held at right angles
to the spring. The iron disc is placed exactly opposite the projecting end of the core of
the primary coil.
Connect the source of electric supply to the outer binding posts of the inductorium in¬
terposing the simple key in the circuit. Close the short-circuiting key of the secondary
circuit. Attach the hand electrodes to the binding posts of the secondary. Place the
secondary coil at right angles to the primary.
Close the simple key. If the interrupter is properly set it will begin to vibiate. On
closing the key the current passes up say, the left hand binding post into and through the
primary coil, comes out by the middle binding post, passes up the spring as far as the set
screw, through this screw and its support to the flat brass band and the right hand bind¬
ing post, and thence back to the source of supply.
As the current flows through the primary coil the core of soft iron wires becomes mag¬
netized and thus attracts the iron disc (the hammer). The spring being, therefore, drawn
away from the tip of the set screw, the circuit is broken and the core becomes imme¬
diately demagnetized. The core ceases to attract the hammer which is then returned to
its former position by the spring. Contact is at once made again between the spring
13
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and the tip of the set screw, the current flows through the primary coil, the core becomes
magnetized, the hammer is drawn toward it, the spring leaves the tip of the set-screw, and
another break of the circuit occurs. These events continue in the same rotation so long as
the simple key .remains closed.
The primary current is thus made and broken automatically, and make and break in¬
duction currents follow each other rapidly. The number of times per second that this
takes place, depends on the vibration period of the spring.
Place the secondary coil at right angles and as far as possible from the primary.
Close the simple key; open the short-circuiting key in the secondary circuit and apply
the electrodes to the tongue. Rotate the secondary toward the primary very slowly un¬
til shocks are distinctly felt.
Does the sensation differ from that obtained with single induced shocks? Note the
position of the secondary in reference to the primary and compare it with that at which
the first single induced shocks were felt. Are the rapidly repeated shocks make or break
shocks?
Unipolar Induction.—Attach a single wire to one of the binding posts of the secondary
coil. Push the secondary coil well over the primary. Connect the primary so as to obtain
tttanizing shocks.
Close the key in the primary circuit and apply the end of the wire connected with the
secondary coil to the tongue. Faint shocks will be felt (although but one wire is attached
to the secondary coil. The explanation of the phenomenon of "unipolar induction" is
that the body acts as a condenser which is charged and discharged alternately through
the electrode in contact with the tongue.
Since there is a possibility that a tisme might be stimulated in the manner just
shown, an open simple key interposed in the secondary circuit would be ineffective in
preventing the passage of induced currents;; accordingly, a short-circuiting key is used
which, when closed, prevents the induced shocks from reaching the electrodes.
THE GRAPHIC METHOD.
The term graphic is given to a method whereby the extent, time of occurrence and
duration of various phenomena are recorded by means of curves or tracings.
I. When the extent, time of occurrence and duration of phenomena can be readily
ascertained, these data are collected at the moment of observation and from them a
curve is constructed. The extent of the phenomenon is indicated on a vertical line divid¬
ed into equal parts representing equal increments of quantity and called an "ordinate."
The time of occurrence and duration are indicated on a horizontal line starting at the bot¬
tom of the vertical one just mentioned. This horizontal line is divided also into equal
parts, representing equal divisions of time, and is called an "abscissa." Usually, as many
ordinates are erected side by side, as there are divisions on the abscissa. The divisions
on these ordinates are obtained by drawing horizontal lines from the points of division
of the first ordinate. The paper is thus divided into a series of squares and is often
called "co-ordinate" paper.
A temperature chart is a familiar example of this kind of graphic record. Dots are
placed at the intersection or ordinates and abscissae and indicate the extent of the tem-
14
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perature at definite times of the day. These dots are connected by lines to faci ita e
reading of the chart in proper sequence.
II. Many physiological phenomena take place so rapidly and are so slight in exten
that unaided observation is insufficient for their study. In order to obtain accurate an
detailed knowledge of such phenomena many ingenious appliances have been devised for
the purpose of causing the organ under study to write a magnified record of its own ac¬
tivities.
In recording the extent, time of occurrence and duration of movements, the following
appliances are commonly employed:
(a) a lever
(b) a kymograph
(c) a chronographic apparatus.
1. Levers are made in diverse forms to adapt them to special purposes. The levers
used during the course will be described at the time they are first used. It may be stated
now, however, that the moving parts of a lever should be as light as possible, that the
lever proper should be rigid in the vertical direction and flexible in a horizontal plane,
and that the writing point should be smooth. The writing point may be made of metal,
glass or parchment paper.
The lever may be allowed to rest lightly on the moving organ or the latter may be
attached to the lever, in which instances, the lever takes up and reproduces changes of
shape, (changes of thickness or of length) which the organ undergoes.
2. Sometimes it is more convenient to transmit the movements of an organ through
a column of air enclosed in a rubber tube. Each end of the rubber tube is connected with
a metallic capsule covered by a rubber membrane; such a device is called a "tambour."
When the membrane of one tambour is pressed inward, the air in the system is compressed
and forces the membrane of the other tambour outward. As soon as the pressure on the
membrane ceases, both membranes return to their position of rest. When the membrane
of one tambour is drawn outward the air in the system is rarefied and the membrane of
the other tambour is depressed. The tambour with which the organ is connected is called
the "receiving" tambour. It is usually provided with a button resting on a disc which is
cemented to the membrane; a hook or a tiny forceps may take the place of the button.
The tambour which serves to reproduce the movements imparted to the membrane of the
receiving tambour is provided with a lever supported by a vertical bearing resting on a
disc which is cemented to the membrane. This tambour is called the "recording" tam¬
bour. The lever magnifies the movements imparted to the membrane.
3. When the phenomena to be studied are successive changes of volume the organ
is enclosed in an air tight receptacle having rigid Avails and in communication by means
of tubing, with a recording apparatus, e. g., a recording tambour, a piston-recorder or a
bellows-recorder. A receptacle adapted for a limb or finger is called a "plethysmograph;"
receptacles for such organs as the kidney and spleen are termed "oncometers" A\diile a
form suitable for the heart has been named a "cardiometer." The medium of transmis¬
sion may be air, oil or water.
4. When pressure and pressure variations are to be studied, some form of "manome¬
ter" is used. The form most commonly employed consists essentially of a U-shaped glass
tube partly filled with mercury, hence called a "mercury manometer." When the pres¬
sure and pressure changes to be studied are slight, water is commonly used instead of
mercury. One limb of the IJ is put in communication with the interior of the organ in
15
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which the pressure resides. This limb is called the "proximal" limb. The other limb—the
"distal" limb—contains a float resting on the surface of the mercury and provided with
a writing style. When the pressure is of su ch character that the mercury in the proximal
limb is depressed, and consequently rises in the distal limb, the pressure is above that of
the atmosphere and is called a "positive" pressure. When the pressure is of the reverse
character—i. e., below that of the atmosphere,—the mercury rises in the proximal limb
and falls in the distal limb. This is called a "negative" pressure. Another and more ac¬
curate form of manometer used especially in the study of rapid variations of pressure, con¬
sists essentially of a recording tambour of very small capacity; this is called a mem¬
brane" manometer. There are other forms, now seldom used, in which a spring takes up
the pressure changes; these are "spring" manometers.
The Kymograph.—The surface on whie A the movements of the writing point are re¬
corded is most generally glazed paper fastened on a cylinder or drum. The glazed paper
is covered with a thin layer of soot obtained by rotating the cylinder through the yellow
part of the flame of a gas burner. If the writing point of a lever is placed
against the cylinder covered with smoked paper and the lever is made to rise and fall, the
soot will be rubbed off by the point. The white line thus produced is a record of the
movement of the writing point. When the cylinder is stationary, the record is in the
form of an arc of a circle and indicates merely the extent of the movement. When the
cylinder rotates at a uniform rate, the rise and fall of the lever are recorded in the form
of a curve. The distance between the two arms of the curve depends partly on the rapid¬
ity of the movement of the lever and partly on the rate of movement of the cylinder. The
rotation of the cylinder is initiated and maintained by clock-work. The speed of rotation
can be adjusted partly by the use of different gears and partly by the use of fans of dif¬
ferent sizes. Inasmuch as the movements are recorded on the moving cylinder in the form
of waves, the apparatus has been named a "kymograph."
The Extent of a Movement.—Since the lever magnifies the movements of the organ
which may be under study, it is necessary that the degree of magnification be known
in order to estimate the actual extent of the organ's movement. The actual extent of
the movement may be determined by the following rule of proportion: The length of the
lever from the axis to the writing point, is to the height of the tracing, as the length of
the lever from the axis to the point of attachment of the organ, is to the movement of
the organ. When a number of measurements are to be made, the same lever having been
used, it is simpler to first find the magnification of the lever by dividing the length of
the entire lever by the part of the lever seen between the axis and the point of attach¬
ment of the organ, and then to use this constant in determining the actual extent of the
organ's movements.
L.
The Time Relation of a Movement.—When a movement is recorded in the form of a '
curve, the time of occurrence and the duration of the entire movement or of any part of
it can be ascertained by means of a "time-marking" or "chronographic" apparatus. The
simplest time-marker consists of a tuning fork, one prong of which is provided with a
writing point. In other forms of time markers the writing point is actuated by a watch
mechanism or by the periodic interruptions of an electric current. In this case, the writ-
16
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ing point is fastened to a movable armature placed above a small electro-magnet. The
electric current is made and broken periodically (1) by the vibrations of a spring, the
end of which is provided with a needle dipping in and out of a cup of mercury; (2)
by the vibrations of a tuning fork, one prong of which is provided with some device for
making and breaking the current; and (3) by the oscillations of a metronome of special
construction. The movements of the writing point of the time-marker are recorded at
the same time as the movements of the lever acted upon by the organ.
If the rate of movement of a given time-marker is 100 per second, each complete move¬
ment seen in the record will equal one-hundredth of a second. By drawing ordinates from
the curve to be studied to the chronographic tracing, the time relations of the curve can
be readily determined.
The Recording of Changes of Electrical Potential.—The activities of the various or¬
gans of the body are accompanied by changes in electrical potential. These can be stud¬
ied by means of suitable galvanometers or electrometers. Observation through a tele¬
scope or microscope sometimes suffices in de ermining the extent of the change of potential.
But when these changes take place in rapid succession, they must be recorded automat¬
ically. This is done by photographing the shadow of the moving part of the galvanometer
or electrometer on a sensitized photographic film traveling at a uniform rate.
The time relations are obtained by photographing at the same time the shadow7 of the
writing style of a time marker.
Construction of a Curve on Co-ordinate Paper.—On a piece of co-ordinate paper con¬
struct a curve showing the passage of food along the intestine. The quantity of food pass¬
ing is expressed in cubic centimeters; the observations were made every half hour. The col¬
lected data are as follows:
Time Quantity
Vt hr 10 cc.
1 hr 30 ec.
1Y* hr 35 cc.
2 hr — 45 cc.
hr 35 cc.
3 hr . 25 cc.
3K hr. ..: ... , 23 cc.
4 hr 20 cc.
4^ hr 17 cc.
5 hr. ... 13 cc.
5^ hr 10 cc.
6 hr 8 cc.
6^ hr 5 cc.
7 hr 3 cc>
The Recording of the Vibrations of a Tuning Fork.—Prepare a cylinder for record¬
ing purposes. The sheets of glazed paper are wider than the cylinder; this is for the pur¬
pose of protecting the bearings of the drum from the smoke. Lay the paper on the table
glazed surface downward and gum one end with a little mucilage. Put the gummed
end away from you and place the cylinder on the paper in such a way that the base of
17
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the shaft shall be at the left and that the paper will project equally on all sides. Bring
the ungummed end against the cylinder, and holding it in position with the thumb of
one hand, take the gummed end between the thumb and fingers of the other hand, raise
cylinder and paper from the table and stick the center of the paper first and then the
sides, making the paper fit against the cylinder as tightly as possible. Rotate the cylin¬
der by rolling the shaft between the thumb and fingers of both hands. Place the rotating
cylinder in the-yellow part of a gas flame and maintain the rotation uniform and fast
enough to prevent the paper from burning. Remove the cylinder from the flame as
soon as the paper has acquired a chocolate-brown color. With a knife, trim the project¬
ing ends of the paper. Replace the cylinder on the clockwork. Mount the tuning fork
on a simple stand in such a way that it will look to the left and that its writing point
will be next to the cylinder. Set the cylinder in motion by releasing the brake on the
fan pinion. The cylinder will rotate at its highest speed; if it does not, pull up the milled
head seen at the right of the shaft. While the cylinder is rotating, pinch the prongs of
the tuning fork together and release them suddenly. The tuning fork will vibrate. Imme¬
diately bring the writing point against the surface of the cylinder with just enough pres¬
sure to obtain a clear rpcord. After one revolution remove the writing point and stop the
cylinder. Note that the distance between the crest of one curve and that of the next
curve is very slight. This represents the distance that the surface of the cylinder travelled
in one-hundredth of a second. Unscrew the set-screw seen at the end of the shaft, and
screw down the ordinary screw until the sleeve of the shaft no longer rests on the fric¬
tion bearing. Set the screw. In this position the drum is pivoted on the steel shaft and
can be spun by hand.
Spin the drum moderately fast, and while it is in motion, record the vibrations of
the tuning fork. Compare the distance from crest to crest in this tracing with that in the
first tracing. Remove the paper from the drum by slipping a large pin between the drum
and paper near the overlap. Move the pin downward and in this way cut ths paper. Pre¬
vent the paper from falling off by holding the upper cut ends with the thumb of the other
hand.
With a sharp pencil write the title of the experiment, the date, and your name on the
smoked paper. In order to make the record permanent, the paper is passed through a
solution of rosin in alcohol. Drain the excess of this varnish in the pan, hang the rec¬
ord and allow it to dry. The alcohol will soon evaporate leaving the soot permanently
fixed against the paper by the rosin. The record can be trimmed with scissors after it has
completely dried.
Trim the record to a convenient size and paste it on the blank page opposite. Pro¬
tect it by a piece of tissue paper stuck at the side of the tracing.
Write a short discussion ol che points of interest in the tracing.
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. V.
IRRITABILITY AND STIMULATION
Irritability.—One of the most characteristic properties possessed by living tissues is
that of irritability. By this is meant the property of responding in a definite manner to
the action of stimuli. The response varies with the nature of the tissue; muscle tis¬
sue when adequately stimulated, responds by a contraction, nerve tissue by the generation
and conduction of a nerve impulse, glandular tissue by the production and discharge of
a secretion. The response may manifest itself as a diminution or arrest of an organ's
activities; to this effect the term "inhibition" is given. Coincidently with the occur¬
rence of these phenomena, there is a liberation of heat and electricity. Thus there is a
transformation of the potential energy residing in the nutritive material found within and
about the tissue cells into kinetic or moving energy which takes the form of mechanical
motion, heat and electricity.
The maintenance of irritability depends upon (1) the proper degree of temperature;
(2) an adequate supply of nutritive material; (3) the prompt removal of waste products.
The proper degree of temperature is insured by the production of heat incidental to
the activity of the various tissues, and by its dissipation in corresponding amounts. The
mechanism of heat production and dissipation is, in homoiothermous animals, controlled
by the nervous system. In poikilothermous animals the temperature of the tissues varies
with that of the surrounding medium, so that the irritability of their tissues is subject to
considerable variations. In general it may be said that low temperatures cause a decline,
and that temperatures higher than the average cause first an increase and later a decline
going on to complete loss of irritability, as the temperature rises. The temperature best
adapted to the functions of an organism, constitutes the optimum or normal temperature
for that organism.
The nutritive material which constitutes the supply of potential energy and the oxy¬
gen necessary for the release of that energy are absorbed from the alimentary canal and
the lungs respectively and carried by the blood to the tissues. This material passes
through the walls of the capillary blood-vessels, becomes part of the lymph, and so comes
in intimate contact with the tissue cells. The cells, therefore, obtain their new supply of
potential energy directly from the lymph; on the other hand, the waste products which
result from the disruption and oxidation of the food and living material in the cells are
received by the lymph and transmitted to the blood stream, whence they are carried to
various organs (lungs, kidneys, skin) whose function it is to eliminate them from the
body.
Stimulation.—Any agent which, when applied to an irritable tissue, is capable of call¬
ing forth the typical activity of that tissue, may be called a stimulus. Since a transfor¬
mation of potential into kinetic energy underlies tissue activity, a. stimulus may likewise
be looked upon as any agent which is capable of bringing about this transformation.
Stimuli have been classified as follows:
1. Mechanical—pinching, tapping, cutting, the vibrations of air.
2. 'Chemical—various chemical substances.
3. Thermic—heat or cold.
19
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4. Electric—galvanic, or induced current.
5. The nerve impulse.
The first four forms of stimulation consisting of external agencies are usually refer¬
red to as artificial forms of stimulation, while the last one, the nerve impulse, being en¬
tirely an animal activity, is sometimes called the physiological stimulus. It should be
borne in mind, however, that some forms of stimulation usually referred to as artificial,
may be likewise physiological. This is particularly the case with chemical stimulation,
which plays an essential role in many of the activities of the body.
Muscle and Nerve Tissue.—Muscle tissue is widely distributed in the animal body and
plays an important part in the maintenance of the life of the organism. The highly ac¬
tive striated muscle, by virtue of its attachment to the bony levers, enables the animal to
perform a variety of movements resulting in a change in the position (1) of one or more
parts of its body in reference to other parts; (2) of the entire body in reference to the
environment. The animal body is thereby able to oppose deleterious influences in its envi¬
ronment, and, if need be, to modify the environment in its struggle for existence.
The visceral muscle (cardiac and smooth muscle) contributes its share of the work in
the functions of nutrition.
Muscle tissue, in common with all the other living tissues, must be stimulated before it
will manifest its characteristic activity.
The normal stimulus for striated muscle is the nerve impulse. But the nerve impulses
are themselves generated through the action of stimuli, viz.: external agencies acting up¬
on the various sense organs of the body. h- ■ ! j
The nerve impulses generated at the periphery are conducted by afferent nerve fibers
to the central nervous system where they may evoke sensations. These in turn may re¬
sult in the development of a volitional effort manifesting itself as a discharge of nerve
impulses and their conduction along efferent nerve fibers to definite muscles. The affer¬
ent nerve impulses generated at the periphery may, however, be reflected to the muscles
by way of efferent nerves without evoking a sensation.
The nervous system, therefore, enables the animal to adapt itself to its environment
by controlling and directing the action of the muscles.
Muscle and nerve tissues are appropriately studied first, because of their importance,
and because their study unfolds fundamental conceptions capable of application in other
parts of physiology. The study of these tissues, moreover, provides a training in elemen¬
tary physiological methods of great value to the modern physician, who should be able
to use instruments of precision with a thorough understanding of their capabilities.
DISSECTION OF THE HIND LEG OF THE FROG.
The muscles and nerves of cold-blooded animals, particularly of the frog, have been
used extensively for purposes of physiological study, for the reason that in these ani¬
mals the tissues retain their irritability for a considerable time after removal from the
body, provided a few simple precautions be observed. The cause of this prolonged vital¬
ity in the absence of blood supply lies in the fact that the rate of metabolism, in cold¬
blooded animals, is very slow. The nutritive material stored up in the tissues as reserve
material is utilized very slowly and the waste material accumulates at a correspondingly
slow rate.
20
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The muscles of the frog which have been generally used for experimental purposes
are the gastrocnemius, the sartorius, the semi-membranosus, the gracilis, and the hyoglos-
sus. The nerve generally used is the sciatic. Muscle and nerve may be studied independ¬
ently of one another, or they may be studied together in their normal relation. In the
latter case the gastrocnemius muscle and sciatic nerve are usually employed, constituting
what is termed a "nerve-muscle preparation."
Preparation of the Frog.—In order to avoid causing pain and to prevent the possible
occurrence of muscular movements which might interfere with the dissection of the frog,
it is necessary to destroy its brain and spinal cord. This procedure is called "pithing."
Proceed as follows: Hold the frog wrapped in a towel, in the left hand, head upward.
Look at the tympanic membrane on each side, draw an imaginary line joining the poste¬
rior extremity of one membrane with that of the other. The point at which this imaginary
line crosses the median line of the body overlies the space between the occipital bone and
the first vertebra. Depress the head of the frog with the left index finger; push a strong
pin through the soft tissues covering the space just mentioned and move the pin from side
to side, thus severing the medulla. Turn the point of the pin forward and push it into
the cranial cavity, move it from side to side and so destroy the brain; finally insert the
pin into the vertebral canal and destroy the spinal cord. Note the attitude of the frog
following this procedure and compare it with that of a frog as yet unpithed.
With a strong scissors sever the body transversely, immediately behind the fore-
limbs. Remove the ventral body wall and the viscera. Look at the dorsal wall of the abdo¬
men and observe on either side of the lower end of the vertebral column three large nerves,
the seventh, eighth and ninth spinal nerves which soon merge to form a main nerve trunk:
the sciatic nerve. The long, slender bone at the end of the vertebral column is the uro-
style (coccyx). Place the pointed blade of the scissors within the pelvis and push it from
above downward until it emerges from the pelvic floor; cut through the pubis. Now divide
the frog longitudinally into two equal halves; start by cutting alongside the urostyle, then
cut through the vertebrae exactly in the middle lfne. Be careful not to injure the nerves
mentioned above, either with scissors or fingers. Leave one leg in its skin and cover it
with a piece of filter paper moistened with normal saline solution so that it may keep in
good condition until needed. Remove the skin from the other leg and place the latter on
a clean plate. With the aid of the diagrams locate the muscles (1) 011 the ventral aspect,
(2) on the dorsal aspect of the thigh and leg. (Figs. 1 and 2).
Dissection of the Sciatic Nerve.—The sciatic nerve, as already stated, is formed by the
union of the seventh, eighth and ninth spinal nerves. It passes out of the pelvis and
then down the thigh along its dorsal aspecl where it lies between the semimembranosus
and the biceps muscles accompanied by the femoral blood vessels. The sciatic nerve sends
branches to the muscles of the entire leg; below the knee it divides into the peroneus and
tibial nerves; the latter sends branches into the gastrocnemius muscle.
Separate the semimembranosus and biceps carefully by tearing the connective tissue
which unites them. The sciatic nerve and femoral blood vessels appear. Free the nerve
gently from the knee to the thigh with the aid of a glass hook. Do not stretch the nerve.
Divide the pyriformis and the ilio-coccygeus muscles. Be careful 111 so doing not to injure
the nerve which lies immediately beneath. Raise the nerve gently, cut the various branches
21
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Fig. 1.—Muscles of the Hind Limb of the
Frog. Ventral View. (G. Bachmann). ad.",
adductor longus; s., sartorius; v. i., vastus interims;
ad.'", adductor magnus; ad.', adductor brevis; r. i.',
rectus interims major; g., gastrocnemius; e.c., ex¬
tensor cruris; t.p., tibialis posticus; t.a., tibialis
anticus.
Fig. 2.—Muscles of the Hind Limb of the
Frog. Dorsal View. (G. Bachmann.) gl., glu¬
teus; v. e., vastus externus; r. a., rectus anterior;
tr., triceps femoris; i. c., ileo-eoccygeus; py., pyri-
formis; h., biceps; s. m., semimembranosus; r. i",
rectus interims minor; g., gastrocnemius; pe.,
peroneus; t. a., tibialis anticus. The biceps and
semimembranosus have been separated to bring the
sciatic nerve, sc. n., into view.
distributed to the muscles of the upper part of the thigh. Continue to isolate the nerve
as far as the points of emergence of the spinal nerves from which it takes its origin. Cut
off the urostyle and then the vertebral column immediately above the seventh spinal
nerve. With forceps lift the half vertebrae and lay the nerve over the gastrocnemius mus¬
cle.
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The Nerve-Muscle Preparation.—With fscissors remove the muscles of the thigh to ex¬
pose the femur from the knee upward. Exercise great care not to cut the sciatic nerve.
Pass one blade of the scissors underneath the tendo Achillis and slide it toward the heel.
Cut through the tendon below its fibro-cartilaginous thickening at the heel. With forceps,
hold the tendo Achillis and pull it gently in an upward direction in order to detach the
gastrocnemius as far as the knee. Cut off the tibio-fibular bone just below the knee joint.
Cut through the femur near the middle. This preparation consisting of a portion of the
femur, the knee joint, the gastrocnemius muscle, the sciatic nerve with the three spinal
nerves from which it takes its origin, and a small portion of the vertebrae constitutes the
"nerve-muscle preparation."
When the contractions of the gastrocnemius are not to be recorded, they may be ren¬
dered more readily visible by leaving the leg entire. In this case, the gastrocnemius, in
contracting, will extend the foot; the movements of the foot will, therefore, be an index
of the contractions of the gastrocnemius. After making the latter preparation, mount a
flat jawed clamp on a simple stand, fasten the femur in the jaws of the clamp. Mount the
adjustable plate-holder above the flat-jawed clamp and bring the glass plate in such a po¬
sition that the sciatic nerve can be laid upon it without stretching. Use the camel's hair
brush wet with saline solution to lift the nerve on the plate. Keep the nerve moist
with normal saline solution.
The irritability of both nerve and muscle and the relative efficiency of the various
classes of stimuli may be shown by means of this preparation in the following experi¬
ments :
THE APPLICATION OF EXAMPLES OF THE VARIOUS CLASSES OF STIMULI TO
THE NERVE.
Mechanical Stimuli.—Pinch the end (central or vertebral end) of the nerve sharply
with forceps. What follows? With the glass rod tap the nerve gently. What follows?
What change takes place in the muscle? Could anything be seen in the nerve? Did any¬
thing occur in the nerve? If so, what was it and what are your reasons for your infer¬
ence? Tap the nerve above the portion crushed with the forceps. Does anything follow?
If not, what explanation can be offered for this lack of response? Are there any nerves in
the body which are normally aroused to activity by mechanical stimuli? Name them.
Cut off the injured portion of the nerve; observe what occurs.
Thermic Stimuli.—Touch the nerve gently a few millimeters from the cut end with a
wire or glass rod heated in the flame of a Bunsen burner. What follows? Stimulate the
end of the nerve. Does anything occur? What is the disadvantage of this form of stimula¬
tion? Cut off the injured portion of the nerve.
Chemical Stimuli.—(Physico-chemical stimuli) — Effect of a strong sodium chloride
solution. Let the free end of the nerve hang from the edge of the glass plate. Put a
small quantity of a 15 per cent solution of sodium chloride in a watch glass and immerse
the end of the nerve into it, Wait a few seconds. What follows? Is there any differ¬
ence in the character of the response from that obtained with mechanical and thermic
stimuli ?
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Effect of Drying.—Bathe that portion of the nerve which came in contact with the
strong sodium chloride solution in normal saline solution. Carefully blot the excess of nor¬
mal saline on the plate. Lower the plate so that the nerve will be exposed to the air on all
sides. The nerve will gradually dry. Observe what occurs. Apply a mechanical stimulus
to the nerve. If no response is obtained, rajse the plate until the nerve once more lies
upon it, and moisten the nerve with a camel's hair brush dipped in normal saline solution.
Wait a few seconds. Apply another stimulus to the nerve. Is there any return of func¬
tion in the nerve? What inference may be drawn regarding the effect of drying upon a
nerve?
Electrical Stimuli.—(1) Effect of the continuous or galvanic current. Attach wires to
the binding posts which connect with the storage battery supplying the laboratory. Place
the simple key in the course of one wire. See that the key is open. Hold the terminals
of the wires between the thumb and index finger of the left hand, being careful that they
do not come in contact with each other. With the aid of the camel's hair brush raise
the nerve and lay it across the terminals. Manipulate the key with the right hand. Make
the circuit. What follows? Allow the currert to flow through the nerve for a few sec¬
onds. Does anything occur? Break the circuit. What follows?
(2) Effect of the induced or faradic current. Arrange the inductorium for obtaining
single induced shocks. Attach the hand electrodes to the secondary coil. Place the secon¬
dary coil at right angles to the primary. Lay the nerve across the platinum tips of the
electrodes. Make, and in a few seconds, break the primary current. Does anything fol¬
low? Rotate the secondary coil slightly toward the primary. Again make and then break
the primary current. Continue to do so until a response follows. Does it occur at the
make or at the break of the primary current? Move the secondary more and more to¬
ward the primary, testing the effect of the nuke and break shocks between each advance of
the secondary. How do the results obtained with the induced current compare with
those obtained with the continuous current?
Arrange the apparatus for obtaining rapidly repeated induced currents. Place the
secondary coil a moderate distance from the primary. Lay the nerve across the electro¬
des. Close the key. What follows? What is the character of the muscle contraction as
compared with that obtained with the single induced shocks. The spasmodic contraction
of a muscle is called "tetanus." The rapidly repeated induced currents which provoke
this form of contraction are often spoken of as "tetanizing current" and the act of ap¬
plying these currents as "tetanization or Faradization." Repeat these experiments with
the secondary coil in various positions.
Representatives of the various classes of stimuli can be applied to the muscle directly
and the irritability of this tissue studied independently of any nerve influence. But be¬
fore this can be done some method must be used which will suspend, with absolute cer¬
tainty, the function of the innumerable nerve branches which supply the individual mus¬
cle fibers. Otherwise, a stimulus applied to the surface or the freshly cut end of a mus¬
cle might act, not only upon the muscle fibers, but also upon the nerve fibers coursing
among them; in such a case it would not be justifiable to infer that the effects observed
were referable to a direct stimulation of the muscle substance only. We shall see later
that a safe and certain method can be employed for the purpose of separating, physiolog¬
ically, the nerve from the muscle fibers.
In experimenting with physico-chemical stimuli it was observed that the immersion
24
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of a part of the nerve in 15 per cent, sodium chloride solution resulted in the generation
of nerve impulses, which, being conducted into the muscle, stimulated it to contractions.
The same results were observed during the drying of the nerve. In the latter case it
is quite obvious that the loss of water is responsible for the disturbance occurring within
the nerve, a disturbance which results first in a generation of nerve impulses and later in
a loss of irritability.
Effect of Strong Salt Solution on the Muscle.—Remove the biceps or the semimembran¬
osus from the frog's thigh, tie one end to a thread and immerse the muscle half-way
into a 15 per cent solution of sodium chloride. What happens as soon as the muscle is
immersed? Keep the muscle suspended half-way in the solution for ten minutes and note
carefully what occurs during that time.
Effect of Distilled Water on the Muscle.—Remove the sartorius muscle from the frog's
thigh. Begin by cutting off its tendinousinsertion into the tibia; with forceps, raise this
free end and snip with the scissors the connective tissue on each side, lifting the muscle
gradually as far as its origin, from which it is then cut off. Suspend the muscle half-way
in distilled water. Does the muscle exhibit any movements? Do permanent changes in
color, length and volume occur?
Osmosis.—The molecules of fluids are in constant and rapid motion. This accounts
for the intermingling of a gas with the air when the gas is exposed to it. Similarly, two
liquids, or solutions brought in contact with each other will intermix so that the mixture
will ultimately become homogeneous. This phenomenon is called "diffusion." The rap¬
idity with which diffusion occurs varies with the nature of the substances concerned and
with the temperature. Substances which have large molecules like starch and albumin
diffuse very slowly. Diffusion is more rapid the higher the temperature.
If instead of bringing liquids in actual contact with each other they are separated
by a parchment membrane, diffusion will occur nevertheless across the intervening mem¬
brane. The passage of the molecules of water from one mass of water to another across
an intervening membrane, is called "osmosis." The passage of dissolved substances is
called "dialysis." Those substances in solution which are capable of passing through a
membrane are called "crystalloids." Those that cannot pass through a membrane are
called "colloids." Give examples of crystalloids and of colloids.
Most membranes, including all animal membranes, permit the passage of water and
of crystalloids in solution. It is possible however to make an artificial membrane that
will allow the passage of water only. Such a membrane is called a "semi-permeable"
membrane. If two masses of water are separated by such a membrane the molecules of
water will pass from one mass to the other in equal numbers in both directions so that
the level of the water on each side of the membrane will remain constant. If the water
on one side of the membrane contains a. crystalloid in solution—say, a one per cent solu¬
tion of cane sugar—water molecules from the other side will pass into the solution in
greater number so that the level of the water 011 each side will change, that is, it will rise
on the solution side and fall on the water side. The reason for this, is that molecules
which are widely separated move very freely and in so doing exert a pressure in all di¬
rections. This pressure is called "osmotic" pressure. As a consequence of the pressure
25
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exerted by the molecules of the dissolved cane sugar, the water continues to enter the
solution until its level has reached such a height that the hydrostatic pressure balances
the osmotic pressure. The difference in the level of the plain water and in that of the
cane sugar solution, at the end of the experiment, measures therefore the amount of the
osmotic pressure. A receptacle provided with a semi-permeable membrane and a glass
tube of suitable length is called an "osmometer."
When the membrane is not perfectly semi-permeable the osmotic pressure, as meas¬
ured with the osmometer, does not reach as great a height as when the membrane is truly
semi-permeable. This is due to the fact that some of the molecules of the dissolved cane
sugar, dialyzing through the membrane, exert a pressure in the opposite direction which
partly neutralizes the original pressure. As more and more of the sugar molecules dialyze
through, the difference in pressure becomes less and when the number of molecules of cane
sugar on each side of the membrane is equal, all evidence of pressure has disappeared. The
reason that an osmotic pressure becomes at all manifest with an imperfectly semi-per¬
meable membrane is that the molecules of the dissolved substance do not pass through the
membrane as rapidly as those of water. The water which accumulates on the solution side
becomes the index of an osmotic pressure.
The temperature being constant, the amount of osmotic pressure depends on the con¬
centration of the solution, i. e. on the number of molecules of the dissolved substance in
a unit volume of solution. In the case of substances which when dissolved separate in
part into ions, the pressure depends on the number of molecules and ions in the solu¬
tion. When several different substances are present in a solution, the osmotic pressure
of the solution is the sum of the osmotic pressure exerted by the molecules and ions of each
individual substance. If one mass of water having a number of crystalloids in solution be
saparated by an imperfectly semi-permeable membrane from another mass of water con¬
taining but one crytalloid in solution but of equal concentration, no changes in the volumes
of water will 'take place, for obviously the osmotic pressure will be the same on each side.
The crystalloids will however, dialyse from one side to the other until the composition of
the solution on each side of the membrane finally becomes identical.
When two solutions of different concentration are separated by a semi-permeable
membrane, water passes from the solution of lesser into that of greater concentration until
the concentration, hence the osmotic pressure, is equal on both sides. The same thing
occurs in the case of a membrane whose semi-permeability is not perfect, with the excep¬
tion that owing to an exchange of the molecules of the dissolved substances, the accumu¬
lation of water on one side of the membrane is not so extensive.
As it is difficult to obtain a membrane which is absolutely semi-permeable, the osmo¬
meter cannot be used for accurate measurements of osmotic pressure. Name two other
methods to determine the osmotic pressure of solutions and state briefly, the principles
on which they are based.
Solutions.—The tissues of the body contain approximately 65 per cent of water. The
water holds in solution a variety of colloid and crystalloid substances. Most of the cells
making up the tissues are surrounded by a membrane which is imperfectly semi-perme¬
able. The cells are in contact with lymph which may be looked upon as an aqueous so¬
lution of crystalloids and colloids. The conditions therefore are such, that an exchange
26
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of material can take place 'between the lymph and the interior of the cells through the
membrane that surrounds them.
When the concentration of the cell contents is the same as that of a solution surround¬
ing the cell, the osmosis of water through the cell membrane takes place as rapidly in one
direction as in the other, so that no physical change occurs in the cells. Since this is the
concentration which is found normally in the blood and lymph, any solution having the
same concentration is often called a "normal" or "physiological" solution. As the os¬
motic pressure of such a solution is the same as that of lymph as well as that of the cell
contents, it is also called an "isotonic" solution. When a solution outside the cell is of
lesser concentration than the cell contents, water passes into the cell where it accumulates
and causes a distention which may go on to rupture of the cell membrane. Such a solu¬
tion has a lesser osmotic tension than lymph and is therefore called a "hypotonic" solu¬
tion. On the other hand, a solution of greater concentration than that of the cell contents
will cause a passage of water from the interior of the cell outward, so that the cell will
shrink. Such a solution having a greater osmotic tension than that of the lymph is called
a "hypertonic" solution.
Explain the results of the experiments on muscle immersed (1) in 15 per cent sodium
chloride, (2) in distilled water, as well as the effect of drying of the nerve. The primary
stimulating effect which was observed may be due to the osmotic changes, but it is also
possible that the salt itself may have acted as the stimulus.
The body fluids contain salts of sodium, potassium and calcium. The one found in
greatest amount is sodium chloride. It is evident from what has been said, that in order
to preserve excised tissues in a physiological condition, a solution isotonic with the blood
or lymph of the animal must be used. A solution containing from 0.6 to 0.7 per cent of
sodium chloride is isotonic with the blood of cold-blooded animals and is often called a
"normal salt solution." One containing 0.9 per cent NaCl is isotonic with the^lood of
warm-blooded animals. Strictly speaking, such solutions are not absolutely normal as they
do not contain the salts of potassium and calcium necessary to balance the tension of the
same salts found in the tissue cells. When an organ is immersed in an isotonic solution of
NaCl, the Ca and K salts diffuse out of the organ and its irritability becomes more or less
impaired. To prevent this occurrence solutions that are more "normal" are employed.
A solution containing NaCl, Ca and K salts in proper proportions is often used and is
called "Ringer's solution," or "physiological salt solution." It consists of 0.7 per cent
NaCl, 0.026 per cent CaCL, and 0.035 per cent KC1. This solution is suitable for cold¬
blooded animals. As modified by Locke, a similar solution can be used in warm-blooded
animals; it contains 0.9 per cent NaCl, 0.024 per cent anhydrous Ca'CL, 0.042 per cent KC1,
and 0.02 per cent NaHC03.
When an organ such as a muscle or nerve is to be kept for only a short time, the use
of the isotonic NaCl solution is sufficient. The organ should not, however, be immersed
in the solution but simply moistened with it. This can best be done with a camel's hair
brush reserved exclusively for this purpose. A frog's muscle which is not needed imme¬
diately can be kept moist by covering it with a piece of blotting paper dipped in the
isotonic salt solution.
Polarization.—The molecules of certain substances, such as the inorganic salts, sepa¬
rate in part into ions when they are dissolved in water. These ions are charged with
27
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electricity, some with positive, others with negative electricity. These ions and the en¬
tire molecules are moving in the solvent in all directions.
When the terminals of two wires connected with the poles of a galvanic battery
are plunged in such a solution the battery current is conducted across the solution from
one terminal—the anodal—to the other terminal—the kathodal. Any solution which is thus
capable of conducting an electric current is termed an "electrolyte." During the flow
of the galvanic current the ions of the soli tion become separated and accumulate at the
surface of the wire terminals in accordance with their electrical charge. The negatively
charged ions are attracted to the anode am are called for this reason the "anions," while
the positively charged ions are attracted to the kathode and are called "kations." Fol¬
lowing this separation of the free ions in the solution, entire molecules split into ions which
in turn become separated through the agency of the electric current.
If wires connected with a galvanic battery are provided with electrodes consisting of
a small plate of platinum, and these be immersed in a solution of copper sulphate, the
current will flow from the positive electrode through the solution to the negative elec¬
trode. After a few minutes it can be shown that the kathode is covered with a deposit of
copper, and that the anode is coated with a layer of small bubbles of oxygen. When the
copper sulphate was dissolving some of its molecules were separated into ions having
charges of electricity. The copper ions have a positive charge, while the sulphions (S04)
have a negative charge. As soon as the current began to flow through the solution the
copper ions were attracted to the kathode, and the sulphions to the anode, but the sul¬
phions reacted with the water of the solution, combined with the hydrogen to form H,S04
and set free the oxygen which was then deposited at the anode. Those molecules of copper
sulphate which had remained entire now split into ions and these in turn underwent sep¬
aration as just described.
When two electrodes are covered and surrounded by ions they are said to be "polar¬
ized." This polarization interferes with the free passage of the galvanic current across
the solution for two reasons: (1) the gas bubbles which accumulate on the anode being
a poor conductor, form a more or less effective barrier betAveen the current and the elec¬
trode; (2) an electric current is generated by reason of the segregation of the ions and this
current flows in a direction opposite to that of the galvanic current. The electric current
which occurs as one of the phenomena of polarization, is called the "polarization cur¬
rent." The battery current Avhich brings about this polarization, may be called the "po¬
larizing current."
When metal electrodes through which an electric current is made to floAv, are placed
in contact with animal tissues they become polarized owing to the fact that the tissue
fluids are electrolytes. The presence of a polarization current can be proved by means of
a galvanometer and by its use as a stimulus.
The Polarization Current Can Act As a Stimulus.—Connect a wire from one of the bind¬
ing posts of the source of electricity to the middle post of a pole-changer (rocking key.)
Connect another wire from the other binding post of the source of electricity to one of the
uprights of the simple key. Run a Avire from the end post of the rocking key opposite
the post already connected, to the other upright of the simple key. Attach the Avires of the
needle electrodes to the simple key. The rocking key connected as explained above acts
as a simple key. Push the needle points of the electrodes into one of the muscles of the
28
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frog's thigh, open the simple key, and make the circuit by closing the rocking key; al¬
low the current to flow for a minute or more. Cut off the polarizing current by break¬
ing the circuit at the rocking key. Immediately thereafter, test the presence of a polari¬
zation current by making and breaking the connection at the simple key. If polariza¬
tion lias occurred what will follow? How long will results be obtainable? The contrac¬
tions will become less and less vigorous and finally disappear as depolarization proceeds.
The polarization current, it will be recalled, flows in a direction opposite to that of
the stimulating current; when metal electrodes are used in physiological investigations and
they remain in contact with the tissues for some little time, this factor will lead to errors
of observation. Furthermore, the separation of ions taking place in the tissue fluids acts
injuriously on the tissues. These disadvantages of metal electrodes can be avoided by the
use of non-polarizable electrodes.
Non-Polarizable Electrodes.—The construction of the usual non-polarizable electrodes
is based on the fact that electrodes of chemically pure zinc, or of amalgamated zinc, im¬
mersed in a saturated solution of zinc sulphate will not polarize. As zinc sulphate is
highly injurious to the tissues it is necessary to interpose between the zinc sulphate and
the tissues some porous, non-metallic material saturated with a non-injurious electrolyte.
The porous material may be a thread of asbestos, a plug of filter paper, a camel's hair
brush, or kaolin. The best electrolyte which can be used is physiological salt solution.
The porous material, saturated with normal salt solution, prevents the zinc sulphate from
reaching the tissues, at least during the time occupied by the average experiment. The
physiological salt solution conducts the electric current into or out of the tissues and not
only obviates the use of metal, but keeps the points of contact wet with an isotonic and
normal fluid.
Suitable electrodes can be prepared by placing an amalgamated zinc rod and saturat¬
ed zinc sulphate solution in a glass tube one end of which is plugged by one of the porous
materials mentioned above saturated with physiological salt solution; the connecting wire
is attached to the zinc rod.
Such electrodes may be used for stimulating purposes or for leading off the tissue
currents to a galvanometer or an electrometer.
A very convenient and satisfactory form of non-polarizable electrodes consists of a
receptacle having the shape of a boot, hence called "boot electrodes." These electrodes
are made of carefully baked, unglazed, potter's clay. When not in use, they are kept
in physiological saline solution in order to become thoroughly saturated with it. When
they are to be used for stimulating purposes, the boots are fastened to the holders which
are mounted on the L-shaped rod of the moist chamber. The leg is then filled half-way
by means of a pipette with saturated solution of zinc sulphate and into this are placed
rods of freshly amalgamated zinc. Wires are run from the zinc rods to those binding
posts of the moist chamber situated immediately beneath the boots. On the upper aspect
of the foot is a well which should be kept filled with normal saline solution during the
entire time that the electrodes are in use. The camel's hair brush is convenient for this
purpose.
As soon as the experiment is over remove the zinc rods, dip them in clean water and
wipe them dry. Rinse out the boot electrodes thoroughly in running water and place
them in the jar set aside for this purpose. This jar contains a large quantity of physio¬
logical salt solution.
29
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The Moist Chamber.—In experiments of long duration it is necessary to take precau¬
tions against loss of water by evaporation from the tissues. This can be done by placing
the organ under study in a chamber, the atmosphere of which is kept saturated with wa¬
tery vapor. Such a chamber is called, accordingly, a "moist chamber.
The moist chamber consists essentially of a circular, porcelain platform having a groove
on its upper surface into which fits a glass cover. This platform is provided with a short
rod by which it may be held on a stand. The platform likewise supports an L-shaped
rod to which is fastened a small clamp consisting of a split screw provided with a nut;
this split screw is for the purpose of holding securely the femur of a nerve muscle prep¬
aration. This clamp may therefore be called the femur clamp. The holder (a double
clamp) which serves to fasten it to the L-shaped rod can be moved horizontally and ro¬
tated in a vertical plane. The L-shaped rod supports likewise two hard-rubber holders for
the reception of non-polarizable electrodes. Provision is made in the floor of the plat¬
form for the fastening of another L-shaped rod to which may be attached holders for
electrodes, etc. Four binding posts, two on each side of the platform, may be seen on
its upper surface. These binding posts are in electrical connection with four other bind¬
ing posts situated on the under surface of the platform. Finally, a circular hole per¬
forates the platform immediately beneath the femur clamp. This hole permits of the
passage of a hook which serves to connect the muscle to a recording lever.
The Muscle Lever.—The muscle lever, which serves to write a magnified record of
the contractions of the muscle, consists of a short piece of nickel-plated brass tubing to
which is attached a strip of aluminum pointed at its free extremity. This pointed end is
slightly curved and forms a weak spring which enables it to remain in contact with tire
smoked paper during the upward moveni nt of the lever. Near the other extremity is a
small steel axle held between two set-screws. A pulley wheel is firmly mounted upon the
axle close to the lever. The groove of this wheel is for the purpose of receiving a thread
or a fine wire, one end of which is secured by passing it through a hole in the side of the
groove and tying it firmly. The other end holds a weight which therefore exerts a pull
near the axis of rotation of the lever. The weight may be made to act more directly on
the muscle. In this case a scale pan is suspended from the double hook seen 011 the lever.
The desired weights are then placed in the scale pan. The upper part of the double
hook is connected to the tendon of the muscle by means of another hook. The lever may
be supported, so as to relieve the muscle from undue pull in the intervals of contraction,
by means of a screw which may be made to press upon the short part of the lever seen
back of the axle. This screw is called the "after-loading screw." When the lever is sup¬
ported by the after-loading screw and the weight is attached immediately beneath the mus¬
cle, the weight does not stretch the muscle previous to the onset of the contraction; this
is called the "after-loaded method" of weighting a muscle.
Owing to the position of the weight—relative to the axis—momentum is imparted to
it, both during the contraction and relaxation of the muscle. This momentum gives to the
lever additional movements which produce errors in the record of the muscle contrac¬
tion. Since momentum varies with the mass and the velocity, it is essential that the
moving parts shall be as light as possible. For this reason the strip of aluminum is often
replaced by a straw provided with a tinsel or parchment paper writing point. A straw
lever, however, possesses the disadvantage of being easily broken. When the weight acts
30
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as near as possible to the axis of rotation of the lever, the tension of the muscle, caused
by the pull of the weight upon it, remains practically uniform during the entire time of
the contraction, and moreover, acceleration of the movement of the lever does not occur.
Since by this method of weighting, the tension of the muscle remains the same during its
contraction, the term "isotonic" has been given to it.
An insulated binding post is fastened to the hard rubber block back of the lever.
This may be used in connection with the flat-jawed clamp when the muscle is to be stim¬
ulated directly. One of the electric wires is attached to the binding post on the flat-
jawed clamp; the other to the binding post on the hard rubber block of the lever. The ten¬
don of the muscle is connected with the double hook by a fine wire whose free extremity
is then attached to the binding post on the hard rubber block.
31
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FACTORS WHICH INFLUENCE THE CONTRACTION
The effect of a Gradual Increase in the Strength of the Stimulus on the Height of the
Contraction.—'Connect the primary coil of the inductorium with the binding posts of the
electric supply so as to obtain single induced currents, interposing a simple key in the cir¬
cuit. Mount the moist chamber and the muscle lever on the adjustable stand. Prepare
the boot electrodes on the L-shaped rod of the moist chamber as explained on page 29
Be very careful not to allow any of the zinc sulphate solution to run outside the elec¬
trodes. If this should happen the electrodes should not be used, but changed for fresh
ones. Run wires from the secondary coil of the inductorium to those binding posts be¬
neath the moist chamber which are in electrical connection with the electrodes. Make a
nerve-muscle preparation and clamp the femur securely in the femur clamp. Fill the
well on the foot of the boot electrodes with normal saline solution by means of the camel's
hair brush. With the same brush place the nerve across the electrodes; see that it is in con¬
tact with both electrodes. Insert the tendonhook at the place of junction of the muscle
with the tendo Achillis. Pass the lever hook through the hole in the platform of the-moist
chamber and connect it with the upper hook on the muscle lever. Moisten filter paper
and place it in the moist-chamber. Put the cover glass in position. Hang the scale pan
with a 10-gram weight to the lower hook on the lever.
Look at the muscle and the thread which connects it to the lever, first from the front
then from the side; the muscle and thread must be in a perpendicular line in both of these
aspects. See that the thread is tense and the lever horizontal. The axle of the lever should
be horizontal also. Screw the after-loading screw downward until it just touches the
lever.
Test the apparatus by making and breaking the primary current, the secondary coil
being at a moderate distance from the primary. Having ascertained that everything is
in working order, proceed with the experiment. Use break induced currents only, since
the object of the experiment is a study of the effect of variations in the intensity, and
not in the character of the stimulus. The make induced current can be prevented from
reaching the nerve by closing the short-circuiting key placed in the secondary circuit, be¬
fore the primary current is made.
Place the stand carrying the moist-chamber and lever in such a way that the point
of the lever comes to rest on the smoked surface of the recording cylinder opposite the
latter's axle. The lever should be at a tangent to the surface of the cylinder and should
point toward the left. Rotate the secondary coil until it is at right angles to the pri¬
mary. Make and then break the primary current. Is there any response? Why? Ro¬
tate the secondary eoil a few milimeteters toward the primary. Make and then break the
primary current. If no response follows, continue to approximate the secondary toward
the primary, making and breaking the primary current between each approximation until
the slightest contraction of the muscle is recorded. Turn the cylinder by hand about half
a centimeter. Bring the secondary coil a few millimeters closer to the primary. Stimu¬
late the nerve with the break shock. The contraction which is recorded is a little higher
than the preceding one. Continue in this way until the contractions remain at a uniform
height despite the further increase in the strength of the stimulus. In a number of ex-
32
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THE EFFECT Of hi GFhWURL INCRERSEIN THE STRENGTH
OF THE CURRENT ON THE HEIGHT
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.FFECrOf R GRADUAL INCRER5E IN THE STRENGTH
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periments, the contractions, after having attained a uniform height, will suddenly reach a
greater height, at which level they again remain uniform, notwithstanding the gradual in¬
crease in the strength of the stimulus.
From the experiment just performed it becomes evident:
(1) That very weak stimuli are unable, singly, to give rise to a nerve impulse. These
very weak stimuli are termed subminimal stimuli. With the further increase in the
strength of the stimulus, the time comes when, from being ineffective, it becomes capable
of causing a response. This is called the "threshold value" of the stimulus.
(2) That the response of the muscle—the height of the contraction—is proportional
within limits, to the strength of the stimulus. A stimulus just sufficient to cause a response
is a minimal stimulus. Such a stimulus, it is believed, gives rise to a weak nerve impulse
which being conducted into the muscle, causes a weak contraction, called a minimal con¬
traction. A stimulus of such strength as to call forth the highest contraction (maximal
contraction) is called a maximal stimulus. Such a stimulus, it is believed, gives rise to a
nerve impulse of high intensity. All stimuli between the minimal and the maximal are
sub-maximal stimuli, and the contractions are called sub-maximal contractions. The first
uniform height attained by the muscle contractions constitutes the "first maximum." The
second uniform height constitutes the "second maximum."
(3) That a relatively weak electric stimulus may cause a maximal response. As a
weak current is less likely to injure living matter than a strong current, the weakest cur¬
rent capable of giving rise to maximal results should always be used. Furthermore, a cur¬
rent of moderate strength will not be so apt to diffuse into the surrounding tissues and
to stimulate organs which do not enter in the problem under study.
Indicate on the smoked paper, by appropriate lettering, the various points of interest
in the record. ;
The Influence of the Load on the Height of the Contraction—In this experiment it will
be necessary to after-load the muscle lever with a considerable weight. As the light
muscle lever, which has been used so far, is not able to bear a heavy weight without
"springing," another more rigid and substantially built muscle lever will be used. This
consists essentially of an iron frame in the shape of a tripod which supports the lever and
its after-loading screw. The tripod is provided at its apex with a clamp by means of
which the flat-jawed clamp may be firmly secured. A large aluminum scale pan is used in
connection with 'his heavy muscle lever. The lever weighs about 2.5 gms. and the scale
pan about 20 gms.
The clamp which serves to hold the flat-jawed clamp is insulated from the tripod
frame. The muscle may be stimulated directly by fastening one wire to the binding
post on the flat-jawed clamp and the other wire to the binding post on the right hand up¬
right supporting the axle of the lever.
Arrange the inductorium for single induced currents with a simple key in the circuit.
Make a gastrocnemius preparation. Fasten the femur in the flat-jawed clamp and the ten¬
don to the lever. Raise or lower the flat-jawed clamp until the muscle lever is horizon¬
tal. Adjust the after-loading screw so that it will support the lever.
With as few trials as possible, find that position of the secondary coil in which the
first maximal stimulus is obtained at the break of the current. This having been deter¬
mined, the inductorium must not be disturbed as the strength of the stimulus must remain
33
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uniform the entire time of the experiment; for the same reason, the primary current
should be broken each time with the same rapidity.
Bring the lever in contact with the smoked paper and rotate the cylinder by hand 3
or 4 cms. so as to obtain an abscissa or base line. Stimulate the muscle with the break
shock. Attach a lead weight (10 gms.) provided with a small wire hook, to the lower
hook on the lever. Move the cylinder by hand about 1 cm. Stimulate the muscle with
the break shock. Remove the weight and put in its stead the large scale pan (weight =20
gms.) Move the cylinder 1 cm. and stimulate the muscle as before. Place a 10 gm.
weight in the scale pan, move the cylinder and stimulate as before. Continue in this way,
adding weights of 10 gms., one at a time, and stimulating the muscle after each addition.
The time will come when the muscle will be unable to lift the load from the after-load¬
ing screw. As soon as this point has been reached, proceed with the two following ex¬
periments :
The Influence of Initial Tension on the Response of the Muscle to a Stimulus of Uni¬
form Strength.—Without disturbing the apparatus used in the preceding experiment, move
the cylinder 5 or 6 cms. Do not remove any weights. Carefully raise the flat-jawed clamp
until the lever is unsupported by the after-loading screw. The muscle in this case is said
to be "loaded," and the weight, acting directly upon it, puts it in a state of tension. Move
the cylinder a few centimeters to obtain an abscissa, and stimulate the muscle as in the
preceding experiment. Does the muscle now contract? What inference may be drawn
regarding the influence of initial tension on the response of the muscle?
The Absolute Muscle Force.—Change the wire on the middle binding post of the pri¬
mary circuit of the induetorium to the right-hand binding post in order to obtain a tetan-
izing current. Find the smallest weight with which the muscle must be after-loaded to
prevent it from contracting wrhen stimulated by a maximal tetanizing current. This
weight measures the "absolute force" of the muscle.
The absolute force of a muscle depends on the number and not on the length of its
fibers. It is therefore proportional to the physiological transverse section of the muscle.
The transverse section is obtain by dividing the volume of the muscle by the average
length of the fibers. The volume is obtained by dividing the weight of the muscle by the
specific weight of muscle tissue, 1.058. For comparative purposes the absolute muscle
force is expressed in terms of 1 sq. cm. For instance, it has been estimated that the ab¬
solute force for 1 sq. cm. of physiological transverse section of the frog muscle is from 0.7
kilogram to 3 kilograms, while for human muscles it has been estimated at 6.24 kilograms;
in other words, a human muscle of the same size and same number of fibers in the aver¬
age cross-section as a frog's muscle would be, at least, twice as powerful as the latter.
Turn your attention, now, to the record of the muscle contractions showing the influ¬
ence of the load on the height of the contraction. Write under the record of each contrac¬
tion, the weight then raised by the muscle. Varnish the tracing and proceed with the
following exercise:
The Influence of a Gradually Increasing Load on the Work Done by the Muscle.—
By the term work, is meant the overcoming of resistance. The forces which commonly re
sist our muscles are connected with the environment and are passive forces, viz., gravity,
friction, cohesion, elasticity, etc. The muscles, by virtue of their attachment to the rigid
<57
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and elastic bony levers of the skeleton and their ability to contract (shorten) when
stimulated, have the power of acting upon the passive forces in the environment. When
the muscles succeed in overcoming these forces, they are doing work. The amount of work
which a given muscle will perform depends upon a variety of factors, ehief among which
may be mentioned: its state of nutrition, temperature, degree '.f tension previous to the on¬
set of the contraction and number of fibers in the physiological cross-section.
In the body, the muscles are loaded by the tonic pull of their antagonists; moreover,
the muscles being a little shorter than the distance they span, are moderately stretched.
They are, furthermore, in a state of slight and continuous contraction, ca^ed tone, caused
by the constant arrival of nerve impulses of low intensity from the spinal cord. The mus¬
cles are therefore in a state of tension previous to their contraction, and this stare of i:.t-
tial tension, we have seen, influences the amount of energy put forth by the muscle.
In many of the movements of the body, the muscles are likewise after-loaded, since
in such instances the force to be overcome does not begin to act until the muscle com¬
mences its contraction.
In the experiment showing the influence of the load on the height of the contraction,
the muscle was after-loaded only. Each time the muscle contracted and raised a weight
against the force of gravity, it did a certain amount of work.
The amount of work done by a muscle during its contractions can be calculated, in
accordance with mechanical principles, by multiplying the weight lifted by the height to
which it is raised. The most convenient unit of measurement in this connection, is the
"gram-millimeter." This unit represents the amount of work done when a weight of one
gram is lifted to a height of one millimeter against the force of gravity.
Calculate the amount of work done by the muscle in the experiment mentioned aboye.
'Determine first, the actual shortening of the muscle, hence the height to which the weight
was raised at each contraction. This is readily obtained by dividing the height (in milli¬
meters) of the records of the contractions by the magnification of the lever. The weight
lifted at each contraction, multiplied by the height to which it was lifted gives the work
done in gram-millimeters.
Arrange the data, as they are obtained, in a table of three columns, as follows:
Weight lifted in
Height to which Weight was
Work done in Gram-
Grams.
lifted in Millimeters
millimeters.
s
Draw an abscissa near the bottom of a piece of co-ordinate paper, and place on this
abscissa, at equal distances apart, the weight in grams used at each successive contrac¬
tion. Draw an ordinate near the leit-hand margin and place at equal distances, numbers
in uniform progression, representing the amount of work done in gram-millimeters.
From the data collected in the table, plot a curve of the work done, using for this
35
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purpose the co-ordinate paper prepared as just mentioned. Note the shape of the curve.
What influence has a gradually increasing load on the amount of work done by an after-
loaded muscle At what time in the experiment did the muscle accomplish the most work?
Compare the influence of the gradually increasing load on the height of the contraction
with that on the work done.
Analysis of a Single Muscle Contraction.—Before it is possible to continue our study
of some of the factors which influence the contraction, it is necessary to analyze the single
contraction in greater detail. In the preceding experiments the contraction was recorded
on the stationary cylinder in the form of an arc of a circle. This method can be used
only to determine the extent of the shortening. It is not possible by this method to de¬
termine :
(1) Whether the shortening began immediately on the application of the stimulus or
not. '01 '' ! i
(2) Whether the time occupied by the entire contraction can be measured or not.
(3) Whether the shortening occupied the same or a different length of time than
the relaxation.
(4) Whether the shortening and relaxation took place with equal rapidity in all
parts of their course, or whether the rapidity of these processes changed at certain points.
These important details of the contraction can be determined by recording the mo¬
ment of stimulation of the muscle and its contraction while the cylinder is in motion. The
time relations of different parts of the contraction can be obtained by recording the vi¬
brations of a tuning fork at the same time as the muscle cor 'Taction.
The contraction will then be recorded in the form of a curve to which the name
"myogram" is given.
Method of Obtaining a Myogram.—First Method. Arrange the inductorium to obtain
single induced currents interposing the simple key and a signal-magnet in the primary cir¬
cuit. The signal-magnet may be mounted on the same stand as the moist chamber or on a
different stand. Make a nerve muscle preparation and arrange it in the moist chamber
as usual. After-load the muscle with 20 gms., using for this purpose two weights tied to¬
gether by a piece of wire terminating in a hook, so as to economize vertical space. With
a T-rule draw a perpendicular line on the smoked paper about 2in. to the right of the over¬
lap. Adjust the muscle lever and the writing style of the signal-magnet so that their
points rest on the same perpendicular line; the signal magnet should write about 2 cm.
below the muscle lever. Find the position of the secondary coil where a maximal break
stimulus can just be obtained. Mount the tuning fork, giving 100 vibrations per sec¬
ond on a stand at such a height that its vibrations will be recorded midway between the
muscle lever and the signal-magnet.
Make the primary current. Start the cylinder rotating at the highest speed obtainable
with t/he clockwork. While one sets the tuning fork vibrating and brings its writing point
in contact with the paper, the other breaks the primary current and immediately there¬
after stops the cylinder.
Repeat this procedure a few times to learn the manipulations necessary for the best
results. The curves which are obtained are difficult of accurate analysis for the reason
that they were taken on a cylinder rotating at too low a rate of speed. W hen the cylin-
36
R hov Qrtff* fray a-tOs Used / @zIoy><~ WadeWrt k' JijfMMff&fih
% S/b'nni-nj Me cxjlmde/ dtf~aslovY 4- -fa-M
purpose the co-ordinate paper prepared as just mentioned. Note the shape of the curve.
What influence has a gradually increasing load on the amount of work done by an after-
loaded muscle At what time in the experiment did the muscle accomplish the most workl
Compare the influence of the gradually increasing load on the height of the contraction
with that on the work done.
Analysis of a Single Muscle Contraction.—Before it is possible to continue our study
of some of the factors which influence the contraction, it is necessary to analyze the single
contraction in greater detail. In the preceding experiments the contraction was recorded
on the stationary cylinder in the form of an arc of a circle. This method can be used
only to determine the extent of the shortening. It is not possible by this method to de¬
termine :
(1) Whether the shortening began immediately on the application of the stimulus or
not. »J!3 i !
(2) Whether the time occupied by the entire contraction can be measured or not.
(3) Whether the shortening occupied the same or a different length of time than
the relaxation.
(4) Whether the shortening and relaxation took place with equal rapidity in all
parts of their course, or whether the rapidity of these processes changed at certain points.
These important details of the contraction can be determined by recording the mo¬
ment of stimulation of the muscle and its contraction while the cylinder is in motion. The
time relations of different parts of the contraction can be obtained by recording the vi¬
brations of a tuning fork at the same time as the muscle cor faction.
The contraction will then be recorded in the form of a curve to which the name
"myogram" is given.
Method of Obtaining a Myogram.—First Method. Arrange the inductorium to obtain
single induced currents interposing the simple key and a signal-magnet in the primary cir¬
cuit. The signal-magnet may be mounted on the same stand as the moist chamber or on a
different stand. Make a nerve muscle preparation and arrange it in the moist chamber
as usual. After-load the muscle with 20 gms., using for this purpose two weights tied to¬
gether by a piece of wire terminating in a hook, so as to economize vertical space. With
a T-rule draw a perpendicular line on the smoked paper about 2in. to the right of the over¬
lap. Adjust the muscle lever and the writing style of the signal-magnet so that their
points rest on the same perpendicular line; the signal magnet should write about 2 cm.
below the muscle lever. Find the position of the secondary coil where a maximal break
stimulus can just be obtained. Mount the tuning fork, giving 100 vibrations per sec¬
ond on a stand at such a height that its vibrations will be recorded midway between the
muscle lever and the signal-magnet.
Make the primary current. Start the cylinder rotating at the highest speed obtainable
with the clockwork. While one sets the tuning fork vibrating and brings its writing point
in contact with the paper, the other breaks the primary current and immediately there¬
after stops the cylinder.
Repeat this procedure a few times to learn the manipulations necessary for the best
results. The curves which are obtained are difficult of accurate analysis for the reason
that they were taken on a cylinder rotating at too low a rate of speed. When the cylin-
36
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exjtinde/ (XSlort 4* -fas't j/eed.
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der revolves more rapidly the curve and ehronographic record are spread out and their
various features are rendered more evident.
Screw down the screw seen at the top of the sleeve carrying the cylinder until the
sleeve is no longer resting on the friction bearing. Set the screw. The cylinder is now
poised on the end of the screw just mentioned and can be made to spin by hand.
Record a contraction on a cylinder spin ling moderately fast, using the method learned
in the preliminary experiments. If the musde should be fatigued use a fresh muscle.
Examine the curve just obtained. Thi; curve or myogram represents graphically the
various phases of the muscle contraction. Taese phases are three in number and can be
indicated on the record, and their duration estimated, as follows: Rotate the cylinder by
hand until the writing point of the muscle lever has passed beyond the curve. The line
thus drawn is the abscissa or base line. With the T-rule, erect a perpendicular through
the point at which the writing point of the s gnal-magnet left the horizontal line. This
perpendicular line—or ordinate—should cut through the abscissa and ehronographic rec¬
ord. Notice that this ordinate strikes a point in front of the muscle curve. As this point
indicates the moment of stimulation, it is evident that some time elapsed between the ar¬
rival of the stimulus and the beginning of the muscle shortening. Erect another perpendic¬
ular ordinate through the point at which the muscle lever rose from the abscissa. All ordi-
nates should cut through the ehronographic tracing. In order to determine the time
occupied by the shortening of the muscle, an ordinate must be drawn from the highest
point in the curve to the abscissa. As the lever in its rise describes an arc of a circle,
the ordinate must likewise be an arc of a circle having the same radius. This ordinate is
therefore drawn with the muscle lever while it is yet in the same position in which it was
during the experiment. Draw a perpendicular line from the base of this ordinate through
the ehronographic tracing. Draw another perpendicular ordinate through the point at
which the muscle lever in its descent crossed the abscissa. This point marks the end of
the relaxation.
The curve is thus divided into three parts or periods which should be indicated on
the smoked paper by lettering the ordinates.
The first period extends from the point of stimulation and the very beginning of the
muscle shortening, and is known as the "latent period." The duration of this period
varies with the conditions of the experiment, e. g., the inertia of the lever, the load to
be raised, strength of stimulus, the elasticity of the muscle, its temperature, fatigue, etc.
Even when mechanical factors are eliminated, a latent period can still be demonstrated.
What is its significance? What is the duration of this period in your experiment?
The second period lies between the beginning of the muscle shortening and the high¬
est point in the curve. It is called the "contraction period," or "period of rising energy."
Note from point to point the inclination of this part of the curve in reference to the abscissa.
What do these changes in inclination indicate as regards the rapidity of development of
the contraction? How long did it take the muscle to pass from the relaxed to the con¬
tracted state?
The third period extends from the highest point in the curve to the point where the
curve crosses the abscissa. It is known a^ the "relaxation period" or "period of de¬
creasing energy." Note the changes in the inclination of this part of the curve from its
beginning to its end and state their significance concerning the rapidty with which the
37
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der revolves more rapidly the curve and chronographic record are spread out and their
various features are rendered more evident.
Screw down the screw seen at the top of the sleeve carrying the cylinder until the
sleeve is no longer resting on the friction bearing. Set the screw. The cylinder is now
poised on the end of the screw just mentioned and can be made to spin by hand.
Record a contraction on a cylinder spin ling moderately fast, using the method learned
in the preliminary experiments. If the musde should be fatigued use a fresh muscle.
Examine the curve just obtained. Thi; curve or myogram represents graphically the
various phases of the muscle contraction. T.iese phases are three in number and can be
indicated on the record, and their duration estimated, as follows: Rotate the cylinder by
hand until the writing point of the muscle lever has passed beyond the curve. The line
thus drawn is the abscissa or base line. With the T-rule, erect a perpendicular through
the point at which the writing point of the s gnal-magnet left the horizontal line. This
perpendicular line—or ordinate—should cut through the abscissa and clhrono graphic rec¬
ord. Notice that this ordinate strikes a point in front of the muscle curve. As this point
indicates the moment of stimulation, it is evident that some time elapsed between the ar¬
rival of the stimulus and the beginning of the muscle shortening. Erect another perpendic¬
ular ordinate through the point at which the muscle lever rose from the abscissa. All ordi-
nates should cut through the chronographic tracing. In order to determine the time
occupied by the shortening of the muscle, an ordinate must be drawn from the highest
point in the curve to the abscissa. As the lever in its rise describes an arc of a circle,
the ordinate must likewise be an arc of a circle having the same radius. This ordinate is
therefore drawn with the muscle lever while it is yet in the same position in which it was
during the experiment. Draw a perpendicular line from the base of this ordinate through
the chronographic tracing. Draw another perpendicular ordinate through the point at
which the muscle lever in its descent crossed the abscissa. This point marks the end of
the relaxation.
The curve is thus divided into three parts or periods which should be indicated on
the smoked paper by lettering the ordinates.
The first period extends from the point of stimulation and the very beginning of the
muscle shortening, and is known as the "latent period." The duration of this period
varies with the conditions of the experiment, e. g., the inertia of the lever, the load to
be raised, strength of stimulus, the elasticity of the muscle, its temperature, fatigue, etc.
Even when mechanical factors are eliminated, a latent period can still be demonstrated.
What is its significance? What is the duration of this period in your experiment?
The second period lies between the beginning of the muscle shortening .and the high¬
est point in the curve. It is called the "contraction period," or "period of rising energy."
Note from point to point the inclination of this part of the curve in reference to the abscissa.
What do these changes in inclination indicate as regards the rapidity of development of
the contraction? How long did it take the muscle to pass from the relaxed to the con¬
tracted state?
The third period extends from the highest point in the curve to the point where the
curve crosses the abscissa. It is known as the "relaxation period" or "period of de¬
creasing energy." Note the changes in the inclination of this part of the curve from its
beginning to its end and state their significance concerning the rapidty with which the
37
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Ck.
^oyam 6^ A. c
t?uYcin/c e~t~A,oci ,
T MUQ9ra.frZ tfviwxtib'e-
<J J I /v/z£ f, od
lwr/'si
l^lyocjrarrt of a/muscle C onfracf/on
Ohfainedi With lh,& rfu -to )n ctti c
t>e v/Vc,e,
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1© s iiwjqa ©rft rvs - lob sfuhr a• uiiT .uol old:-. s«ii <><ui f-'Shsdw :-.!q -
faisoK 'j j
lo *i, .• it mq tiiiJ . ;[.? noii -oq j.. ■ m twin* ■ ,ao •
*ai/ux i < ■ ; ■ ■ -
.
■ fjffd • lo • tis'jm «i hai^k ■ ■ " ; o i ■ i ri?
t dqre ■ I ' ij <-?*'.•- ' II -:}( ' T!. -'E' t -- - B
.' v (qqj - to -1 .-■.<Ifehfi robtirf-/.: ■ ■ ■ > fti
•H ' '.woivrrtr ft ai .;r, / U ;j. <: >*, n-i lq tia .0 . . r . u r •
jrfj .• j i'it *ds I '" : i ' <• tl : !• od I < ' i
lit-}* ol bewollii j»i n ; ■ • . • : , i . .<
'
jjf;r ' noiii*, . | tli) h> M - ' I 'nil - »J 0 1 >0 9
muscle relaxes throughout the period. How much time was occupied by the muscle in
passing from the contracted to the relaxed state?
What was the duration of the whole contraction process? Is this duration the same
in all muscles of the same animal? Is it the same in homologous muscles of different
animals? What differences are there in the contraction of red and of white muscles?
When a number of muscle curves are taken for the purpose of determining the effect
of various intensities of a same factor, their comparison is facilitated by starting them
from a point common to all. Stimulation must, of course, occur at exactly the same point
on the smoked paper. This can be accomplished by making the cylinder open the pri¬
mary circuit of the inductorium automatically at a definite point in its rotation. In order
that the curves shall be strictly comparable the spinning of the cylinder must be uniform
in speed at each revolution. These conditions can be fulfilled with the following device:
Automatic Spinning Device.—The object of the device is to provide <a simple and ac¬
curate means of automatically spinning the cylinder of a kymograph for one revolution.
The essential parts of the device consist of a "trigger" to release and arrest the cylinder
and an ordinary rubber band, one-fourth inch wide. In order that the kymograph may
remain in position it is firmly clamped on a special stand made stationary by screwing it
into a brass plate embedded into the table top. Three white dots on the upper surface of
this stand indicate the position the three feet of the kymograph must occupy.
Fasten the paper on the drum in such a way that its glued section will be opposite the
pin screwed into the bottom of the drum. Smoke the paper and trim both edges. Mount
the trigger firmly on the stationary stand in such a position that the pin at the base of
the cylinder will pass along the curve of the spring with slight friction and be stopped by
the projecting stop. Fasten a double clamp to the axle below the drum so that the pin at
the base of the drum being in contact with the stop of the trigger, the double clamp
will be parallel with the edge of the table; the free jaw of the double clamp must
look to the left. Pass one end of the rubber band into this jaw and the other end around
an elbow wire attached to the binding post on the base of the kymograph. On the left
hand side of the cylinder mount a simple key on a stand by means of a burette clamp;
place it in such a way that the pin of the cylinder will strike the handle of the simple key
and thus open it as the cylinder rotates. Connect the electrical source of supply with pri¬
mary of inductorium, simple key and signal magnet as in the previous experiment. By
rotating the drum by hand from left to right until the pin has passed the trigger stop, the
rubber band will be twisted around the axle. The drum can then be allowed to spin for
one revolution by simply pressing on the trigger with the thumb and then releasing it. Au¬
tomatic stimulation by a break induction shock will be obtained when the hard rubber
handle of the simple key is struck by the pin projecting from the bottom of the cylinder
as the latter rotates.
Second Method of Obtaining a Myogram.—Make a nerve-muscle preparation and
mount it in the moist chamber as usual. Clamp the moist chamber to an adjustable stand;
the signal magnet should be mounted on the same stand below the muscle lever. Connect
the secondary coil with the electrodes of the moist chamber. Find the position of the sec¬
ondary coil where a maximum break stimulus will be obtained. Open the simple key. Ro¬
tate the cylinder from left to right to twist the rubber band. Draw a perpendicular line
on the smoked paper with the T-rule opposite the axle. Adjust the writing points of the
muscle lever, tuning fork and signal magnet on this perpendicular line. Close the simple
38
■
"
: -t ■ ' >->'i ■ \ : i '
■
.
key. Start the tuning fork vibrating and release the drum by pressing upon the trigger.
The myogram will be recorded automatically. The position of the curve on the smoked
paper will be determined by the position of the simple key. Remove the tuning fork and
signal magnet from contact with the paper. Disconnect the rubber band. Rotate the cylin¬
der by hand to obtain an abscissa. Draw ordinates as in the preceding experiment. The
muscle lever must not be moved to and from the cylinder in any other way than by mani¬
pulation of the screw at the base of the stand.
Letter the ordinates and estimate the duration of the various phases of the contraction.
The Effect of Repeated Contraction on the Irritability of the Muscle.—When a mus¬
cle is made to contract repeatedly it passes in time, into the condition called "fatigue."
By this term is meant a decrease in irritability and consequent diminished capacity for
doing work due to more or less prolonged functional activity. The causes responsible for the
production of fatigue are: (1) the consumption of energy-holding substances, and (2) the
accumulation of waste material. The energy-holding substances which are utilized by the
muscle to supply the energy of the contraction are primarily dextrose and its precursor,
glycogen. The waste material formed during the contraction and which, it is believed, is
especially concerned in the production of fatigue, consists of sarcolatic acid, carbon dioxide
and monopotassium phosphate. If a fatigued muscle is allowed to rest, the energy-holding
substances will be replaced, the waste products will be more completely oxidized and re¬
moved, and the normal irritability of the muscle restored.
When a muscle is deprived of its circulation, as is the case in an excised muscle, the
only energy-yielding substances which it can obtain are those stored as a reserve in the
muscle fibers and those still present in the lymph spaces. Owing to the restricted supply
of oxygen available and the absence of a circulation to carry off the waste material there
will be a rapid accumulation of the intermediary products of dextrose metabolism, e. g.,
sarcolactic acid. These two factors, therefore, namely, (1) the limited supply of energy-
holding substances and of oxygen, and (2) the retention of the waste material, contribute
in an excised muscle, to bring about the condition of fatigue more rapidly than in a mus¬
cle in its normal relations.
The Development of Fatigue in an Excised Muscle.—Prepare the cylinder for record¬
ing as explained in the preceding experiment. Arrange the kymograph for automatic
spinning. Place the simple key, mounted for automatic break, well toward the front. Run
a short wire from one of the binding posts of the source of supply to the middle binding
post of the inductorium; run the longest wire from the other binding post of the source of
supply to the contact binding post of the simple key. Mount tihe signal magnet on a sim¬
ple stand and connect one of its wires with the left hand binding post of the inductorium
and the other wire with the remaining binding post of the simple key. The terminals of
the signal magnet wires are thus easily accessible and can be disconnected without dis¬
turbing the apparatus.
Rotate the cylinder by hand from left to right so as to twist the rubber band. Draw a
perpendicular line on the smoked paper in the usual position. Adjust the writing points of
the signal magnet and of the tuning fork to the perpendicular line. Leave ample space above
for the myograms. Close the simple key and take a simultaneous record of the instant of
break of the primary current and of the vibrations of the tuning fork. Remove the signal
39
key. Start the tuning fork vibrating and releas
The myogram will be recorded automatically,
paper will be determined by the position of the
signal magnet from contact with the paper. I
der by hand to obtain an abscissa. Draw ordii r.
muscle lever must not be moved to and from '
pulation of the screw at the base of the stand.
Letter the ordinates and estimate the dura: ■
The Effect of Repeated Contraction on the
cle is made to contract repeatedly it passes i.
By this term is meant a decrease in irritability
doing work due to more or less prolonged func . o
production of fatigue are: (1) the consumpt:
accumulation of waste material. The energy-h ;
muscle to supply the energy of the contractu
glycogen. The waste material formed durir
especially concerned in tihe production of fa:
and monopotassium phosphate. If a fatigu*
substances will be replaced, the waste produ
moved, and the normal irritability of the
When a muscle is deprived of its circuk
only energy-yielding substances which it cai
muscle fibers and those still present in th
of oxygen available and the absence of- a cb
will be a rapid accumulation of the interme
sarcolactic acid. These two factors, therefc
holding substances and of oxygen, and (2)
in an excised muscle, to bring about the
cle in its normal relations.
The Development of Fatigue in an 1
ing as explained in the preceding experi
spinning. Place the simple key, mounted
a short wire from one of the binding post:
post of the inductorium; run the longest v
supply to the contact binding post of th
pie stand and connect one of its wires wi
and the other wire with the remaining 1
the signal magnet wires are thus easily
turbing the apparatus.
Rotate the cylinder by hand from lef
perpendicular line on the smoked paper b, 1 ;
the signal magnet and of the tuning for] t<> :
for the myograms. Close the simple key t nk t h -nn-
break of the primary current and of th v c. » «
39
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magnet from the circuit and replace it by a long wire; be careful in doing this not to move
the simple key.
Make a nerve muscle preparation, place it in the moist chamber and observe the
usual precautions to preserve it in good condition throughout the experiment. Mount the
moist chamber on the adjustable stand; connect it with the secondary coil and adjust the
writing point of the muscle lever to the perpendicular line just above the tracings just ob¬
tained. Find the position of the secondary coil of the inductorium where the first evi¬
dence of a maximal break stimulus is obtained. Record one contraction. Remove the
writing point from the smoked paper by means of the screw at the base of the stand. Ro¬
tate the cylinder to twist the rubber band.
Make and break the primary current by means of the simple key and thus make the
muscle contract forty-nine times at the rate of once a second. Be careful not to move the
key. Return the writing point exactly to the perpendicular line and record the fiftieth con¬
traction. Repeat these manipulations, recording every fiftieth contraction, until the mus¬
cle no longer responds to the stimulus.
As soon as this point has been reached, disconnect the wires attached to the secondary
coil, and put in their stead the wires in connection with the hand electrodes. Do this as
quickly as possible. Stimulate the muscle directly by means of the band electrodes, using
the same strength of stimulus as was used during the experiment. Does the muscle re¬
spond? It is a well known fact that nerve fibers cannot be fatigued. Where, then, in the
neuro-muscular apparatus, are the first effects of fatigue felt? After a little time, stimu¬
late the nerve again. Does the muscle contract? If so, what explanation can be offered
for the recovery from fatigue?
'Cut the muscle across and test the chemical reaction of the cut surface with litmus
paper. Compare this reaction with that of a muscle immediately after it has been re¬
moved from the body.
A chronograhic record should be placed beneath the curves. Varnish the tracing.
Study the curves carefully. What effect has the development of fatigue (1) on the height
of the contraction, (2) on the three periods of the contraction? In what respects does
the development of fatigue in mammalian muscle differ from that of cold-blooded mus¬
cle?
The Study of Fatigue in Human Muscles.—The development of fatigue, and, inci¬
dentally, the amount of work which a human muscle can do under a variety of conditions
can be studied by means of an apparatus called an "ergograph." Two types of ergo-
graphs have been devised. In one type a stiff spring opposes the contraction of the mus¬
cle. By graduating the spring with known weights the amount of work which the mus¬
cle does can be calculated. In the other type a weight is raised at each contraction of
the muscle. The distance through which the weight is raised is recorded on the smoked
paper without magnification. As the muscle should be made to contract at short intervals,
the beat of a metronome is used as a signal for the contraction.
Obtain an ergographic record with the spring ergograph, or with Hall's weight ergo¬
graph, making the muscle contract once every two seconds. Notice that the weight in its
descent is supported by an air cushion so th at the muscle does work during the contrac¬
tion, and none during the relaxation. The muscle studied with both types of ergograph
is the flexor digitorum sublimis.
40
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magnet from the circuit and replace it by a long wire; be careful in doing this not to move
the simple key.
Make a nerve muscle preparation, place it in the moist chamber and observe the
usual precautions to preserve it in good condition throughout the experiment. Mount the
moist chamber 011 the adjustable stand; connect it with the secondary coil and adjust the
writing point of the muscle lever to the perpendicular line just above the tracings just ob¬
tained. Find the position of the secondary coil of the inductorium where the first evi¬
dence of a maximal break stimulus is obtained. Record one contraction. Remove the
writing point from the smoked paper by means of the screw at the base of the stand. Ro¬
tate the cylinder to twist the rubber band.
Make and break the primary current by means of the simple key and thus make the
muscle contract forty-nine times at the rate of once a second. Be careful not to move the
key. Return the writing point exactly to the perpendicular line and record the fiftieth con¬
traction. Repeat these manipulations, recording every fiftieth contraction, until the mus¬
cle no longer responds to the stimulus.
As soon as this point has been reached, disconnect the wires attached to the secondary
coil, and put in their stead the wires in connection with the hand electrodes. Do this as
quickly as possible. Stimulate the muscle directly by means of the band electrodes, using
the same strength of stimulus as was used during the experiment. Does the muscle re¬
spond? It is a well known fact that nerve fibers cannot be fatigued. Where, then, in the
neuro-muscular apparatus, are the first effects of fatigue felt? After a little time, stimu¬
late the nerve again. Does the muscle contract? If so, what explanation can be offered
for the recovery from fatigue?
'Cut the muscle across and test the chemical reaction of the cut surface with Ltmus
paper. Compare this reaction with that of a muscle immediately after it has been re¬
moved from the body.
A chronograhic record should be placed beneath the curves. Varnish the tracing.
Study the curves carefully. What effect has the development of fatigue (1) on the height
of the contraction, (2) on the three per iods of the contraction? In what respects does
the development of fatigue in mammalian muscle differ from that of cold-blooded mus¬
cle?
The Study of Fatigue in Human Muscles.—The development of fatigue, and, inci¬
dentally, the amount of work which a human muscle can do under a variety of conditions
can be studied by means of an apparatus called an "ergograph." Two types of ergo-
graphs have been devised. In one type a stiff spring opposes the contraction of the mus¬
cle. By graduating the spring with known weights the amount of work which the mus¬
cle does can be calculated. In the other type a weight is raised at each contraction of
the muscle. The distance through which the weight is raised is recorded on the smoked
paper without magnification. As the muscle should be made to contract at short intervals,
the beat of a metronome is used as a signal for the contraction.
Obtain an ergographic record with the spring ergograph, or with Hall's weight ergo¬
graph, making the muscle contract once every two seconds. Notice that the weight in its
descent is supported by an air cushion so th at the muscle does work during the contrac¬
tion, and none during the relaxation. The muscle studied with both types of ergograph
is the flexor digitorum sublimis.
40
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The Demonstrator will give the necessary directions in the use of the ergographs.
What is the difference in the results obtained with the two types of ergographs?
The Influence of Different Temperatures on the Muscle Contraction.—The activities
of living matter are in great part conditioned by the intensity of the chemical processes
which take place in it. As the rate of chemical action changes with the temperature it
is important to know how the activities of living matter are affected by various degrees
of temperature. Animals whose body temperature follows the variations which occur in
their surrounding medium (cold-blooded animals), will naturally be more often subjected
to the influence of temperature changes than animals having a constant body tempera¬
ture (warm-blooded animals). But the latter are not wholly free from more or less ex¬
tensive temperature changes. Exposed parts of the body when subjected to intense cold
may suffer in their physiological and anatomical integrity; the same is true of the effect
on tissues of a high degree of heat such as may be present during fever. The follow¬
ing experiment will serve to illustrate the modifying influence of heat and cold upon the
activity of living matter:
Apparatus.—The apparatus consists of an L-shaped metallic rod provided with a hook
at one extremity and a binding post at the other. This L-shaped rod is to be clamped
to the adjustable stand at such a height that the aluminum cup—which is to contain Ringer's
solution—can be slipped underneath without spilling the solution. The second part of
the apparatus consists of a copper wire fastened to a binding post screwed in an insulat¬
ing vulcanite bushing set in a clamp. To this wire is attached a linen thread terminat¬
ing in a fine wire hook. The third part of the appararns consists of a balanced lever, the
short and long arms of which are perforated with a number of pin holes. Fasten the bind¬
ing post support about an inch above the L-shaped rod; clamp the balanced lever above
and in such a position that its short arm will be directly above the hook seen at the ex¬
tremity of the L-shaped rod. Place a folded towel on the table beneath the L-shaped rod to
absorb any solution that might be accidentally spilled.
Experiment: Obtain a simultaneous record of the instant of break of the primary cur¬
rent and of the vibrations of the tuning fork. (Follow the instructions contained in the
first two paragraphs of "The Development of Fatigue in an Excised Muscle"). Connect
one wire of the secondary coil with the L-shaped rod and the other wire with the binding
post on the clamp.
Remove a gastrocnemius muscle and fasten its tendon end to the hook of the L-shaped
rod. Pass the end of the copper wire through the upper end of the muscle and bend it
upward so that it will not slip out. Pass the fine wire hook at the end of the thread into
one of the holes of the short arm of the lever a moderate distance from the axle. Counter¬
poise the muscle with ia suitable weight. Mo isten the muscle with saline solution.
Find the position of the secondary coil where the first maximal break shock can be ob¬
tained. This having been determined, the secondary coil must not be disturbed. Ringer's
solution has been placed in bottles and these have been packed in a freezing mixture of ice
and salt. Cool the aluminum beaker and fil 1 it nearly full with the cold solution. Carry
the breaker by the brim as the heat of the hand would otherwise raise the temperature of the
solution. Immerse the muscle in the solution; while the muscle is cooling, ascertain the
41
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THE CONTINUOUS CONTRACTION.
The Summation of Muscle Contractions.—The single muscle contraction which we have
studied so far is not the characteristic activity of muscle in its normal relations. The
muscle contractions as they take place in the body are always sustained contractions.
The muscle during its activity is continuously contracted; this is true of even the short¬
est possible contraction for it occupies always a longer time than does the single contrac¬
tion obtained experimentally by means of a single induction shock.
The continuous contraction, however, being of a complex character, it was necessary
to use the simplest form of muscle activity—the single muscle twitch—to study the reac¬
tions of muscle tissue to various factors.
The object of the following experiments is to determine how the normal, more or less
prolonged and continuous contraction, is produced.
When a muscle is stimulated by a number of successive stimuli, the character of the
response of the muscle varies in accordance with the rapidity with which the stimuli
follow one another. When the time interval between the successive stimuli is equal to, or
greater than, the total time of the contraction process, each muscle contraction is com¬
pleted before the following one begins. This is especially true of the first contractions. If
temperature of the solution. It should be 0° C. Let the muscle remain in contact with the
cold solution for three minutes. Remove the solution and immediately record the contrac¬
tion. Remove the writing point from the cylinder by means of the screw at the base of the
stand. Examine the curve and write over it the temperature. Raise the temperature of
the solution to 5° C., by holding the beaker in both hands. Immerse the muscle in the
solution for three minutes, at the end of which time remove the solution and immediately
record the contraction. Record contractions of the muscle in the same manner at tempera¬
tures of 10°., 15°., 20°., 25°., 30°., 35° C., writing the temperature over each curve. The
temperature of the solution is raised by heating it over the flame of a Bunsen burner. Care
must be taken not to move the base of the adjustable stand. Remove the rubber band.
Finally raise the temperature of the solution to 45° C. Turn the cylinder by hand
until the writing point of the balanced lever is about 1 cm. to the left of the point of stimu¬
lation. Immerse the muscle in the solution. Let the muscle remain in the solution until
it has ceased shortening. Turn the cylinder by hand about 5 cm. Remove the writing
point from the smoked surface.
Stimulate the muscle. Does it respond? How does the muscle feel to the touch? The
change which has taken place in the muscle is known as "heat rigor," The most obvious
phenomenon accompanying this condition is a coagulation of the muscle proteins. Discon¬
nect the muscle from the apparatus. Blot the Ringer's solution which covers it, and cut it
transversely. Test the cut surface with litmus paper. What is the chemical reaction of a
muscle in heat rigor? What is the chemical reaction of fresh muscle when tested with lit¬
mus paper? Varnish the tracing and study in detail the influence of temperature on the
contraction. Note (1) the influence of the different temperatures on the height of the
contractions; (2) on the length of the latent period; (3) on the time occupiedTjy the short¬
ening; (4) on the time occupied by the relaxation. Is there any variation in your experi¬
ment from the average result? At what temperatures do the muscle proteins of warm¬
blooded animals coagulate? What is the temperature of the body in hyperpyrexia?
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the stimulation is kept up at the same rate, there will be observed a gradual increase in
height of the contraction for a short period of time. This is the "Treppe" or "stair-case
effect," the result of an increased irritability of the muscle caused by the primary stimulat¬
ing effect of the products of fatigue. Later on the condition known as "contracture" may
develop.
If the time interval between sucessive stimuli is less than the total time of the con¬
traction process, the muscle will not have completely relaxed before it is again stimulated
and the result is a series of contractions which superimpose themselves upon the first. The
muscle will shorten more and more until a maximum height has been reached which is
greater than could be obtained with any single stimulus of maximal strength. To this
superposition of contractions the term "summation of contractions" is given. Successive
stimuli produce their greatest effect when they stimulate the muscle during the last third
of the period of rising energy.
The facts just stated are illustrated in t he following experiment:
Experiment.—Arrange the kymograph for automatic spinning as in the experiment
performed in the study of the single muscle contraction. An adjustable, double-contact
key is placed in the path of the pin instead of the simple key. The contacts can be ad¬
justed at such angular distance from each other that the first contraction of the muscle will
have time to complete itself before the second begins. By bringing the contacts closer
to each other the second stimulation of the muscle can take place at any point in the
phases of the first contraction. Interpose a signal magnet in the primary circuit.
Prepare a nerve-muscle preparation, place it in the moist-chamber as usual, and con¬
nect the tendon to the lever properly weighted. Place the secondary coil at such a dis¬
tance from the primary that both make and break shocks will be effective. Adjust the
writing points to the smoked surface, close the simple key, set the cylinder rotating, and
record the contractions. Smoke another paper. Move one contact closer to the other.
Record the contractions. Repeat this on different papers several times, each time moving
one contact closer to the other, until the second contraction begins at the apex of the first.
Compare the height of the summated contraction with that of the first contraction through¬
out the series. At which time w,as the highest contraction obtained?
Tetanus.—By tetanus is meant a more or less continuous contraction of ia muscle, the
result of the arrival of successive stimuli at intervals less than the time of the contract
tion process. Tetanus will be incomplete or complete, in accordance with the rate at
which the stimuli follow each other. If the time of the contraction process of a muscle,
e. g., the gastrocnemius, is one-tenth of a second and stimuli are sent into the muscle
la.t intervals of, say, one-fifteenth of a second, the relaxation will be interrupted by the
arrival of a stimulus which will cause the muscle to contract again; the following relax¬
ation will likewise be interrupted by the next stimulus and the muscle will again contract.
The muscle will therefore exhibit alternately contractions and relaxations of a slight
extent, the muscle remaining, in the meanwhile, partially contracted. To this form of mus¬
cle activity the term "incomplete tetanus" or "clonus" is given. The muscle will con¬
tinue to respond to each stimulus until fatigue sets in, whereupon it will relax despite
continued stimulation.
43
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If the time interval between the successive stimuli be gradually decreased the alter¬
nate contractions and relaxations will decrease in extent until finally they will become
so small as to be practically invisible and the muscle will then appear to be continuously
and steadily contracted. To this form of muscle activity the term "complete tetanus" is
applied. It can be shown, however, that a muscle during complete tetanus is still under¬
going alternate contractions and relaxations, but of such minute extent as to constitute
vibrations. By what means may these vibrations be detected? Are our voluntary and re¬
flex contractions of skeletal muscles, states of tetanus? How may this be proved? What
inference may be drawn concerning the character of the discharge of nerve impulses from
the nerve cells which stimulate skeletal muscles to contraction?
The Development of Tetanus.—In studying the development of tetanus it is necessary
to have some means of sending successive stimuli into the muscle at regular intervals,
the duration of which can be changed. These conditions can be met by the use of the
vibrating interrupter already described under the head of chronographic apparatus, page
17.
Clamp the mercury cup to a simple stand, about 3 inches from the base; clamp the
spring holder to another simple stand, about 4 inches from the base. Fasten the spring
in the holder in the position at which it will vibrate five times per second; (the mark 5
must be exactly on the right edge of the holder.) Clamp the electromagnet immediately
above the spring to the left of the holder. Be careful that the core of the magnet does
not touch the spring. The apparatus must be mounted on the simple stands in such a
way that the batters' straight sides are opposite each other.
The vibrating interrupter and the simple key are to be placed in the primary circuit
of the inductorium as follows: Run a wire from one of the binding posts of the source
of supply to the binding post above the electromagnet. Run another wire from the mer¬
cury cup to the middle post of the inductorium. Connect the other binding post of the
source of supply with the left hand binding post of the inductorium, interposing the sim¬
ple key.
Adjust the kymograph for a moderately slow speed (largest fan with high speed
gear.)
Make a nerve-muscle preparation and mount it in the moist chamber as usual. Close
the simple key and find the position of the secondary coil where the first maximal break
shock is obtained, making and breaking the current by moving the needle of the spring in
and out of the mercury by means of the finger. Place the point of the lever in contact
with the smoked paper. Close the short-circuiting key in the secondary circuit. Start the
spring vibrating and the cylinder revolving. Open the short-circuiting key and allow the
muscle to contract about six times. Close the short-circuiting key. Stop the cyl¬
inder, and open the simple key. Adjust the spring and mercury cup so as to obtain 10
stimuli per second. Close the simple key, and repeat the manipulations just described.
Obtain records with stimuli sent into the nerve iat the rates of 15, 20, 25, 30 and 50 per
second. Write under the curves the rate of stimulation per second.
Describe the various points of interest in the experiment. Is there any evidence of
summation effects? At what time in the experiment did this become manifest? Did it
become more marked in the following curves? What rate of stimulation was necessary to
produce complete tetanus? How does the time interval between the successive pqimuli
44
If the time interval between the successive
nate contractions and relaxations will decrease
so small as to be practically invisible and the mi
and steadily contracted. To this form of musch
applied. It can be shown, howTever, that a mu
going alternate contractions and relaxations, b
vibrations. By what means may these vibration
flex contractions of skeletal muscles, states of t€
inference may be drawn concerning the chara
the nerve cells which stimulate skeletal muscles
The Development of Tetanus.—In studying
to have some means of sending successive stim
the duration of which can be changed. These
vibrating interrupter already described under
17.
Clamp the mercury cup to a simple stand,
spring holder to another simple stand, about
in the holder in the position at which it will
must be exactly on the right edge of the holde
above the spring to the left of the holder,
not touch the spring. The apparatus must
way that the batters' straight sides are opposil
The vibrating interrupter and the simple
of the inductorium as follows: Run a wire
of supply to the binding post above the electr
cury cup to the middle post of the inductorium
source of supply with the left hand binding
pie key.
Adjust the kymograph for a moderately
gear.)
Make a nerve-muscle preparation and mo
the simple key and find the position of the se
shock is obtained, making and breaking the
and out of the mercury by means of the fin.
with the smoked paper. Close the short-cm
spring vibrating and the cylinder revolving,
muscle to contract about six times. Clos
inder, and open the simple key. Adjust th
stimuli per second. Close the simple key, a
Obtain records with stimuli sent into the n
second. Write under the curves the rate oi
Describe the various points of interest
summation effects? At what time in the e:
become more marked in the following curv
produce complete tetanus? How does the 1
4
.
.
necessary to produce complete tetanus compare with the time of a single contraction of
the frog's gastrocnemius? What influence would (1) fatigue, (2) a low temperature have
on the development of tetanus? Why?
THE INDEPENDENCE OF MUSCLE IRRITABILITY.
Claude Bernard's Curara Experiment.—The preparation used so far in the study of
the reactions of muscle to various agencies, has been the nerve muscle preparation and
the muscle was stimulated indirectly through its nerve. It is not possible with such a
preparation to determine whether the irritability of muscle depends or not upon that of
the nerve which is in anatomical and physiological connection with it. The application of
a stimulus to the muscle directly cannot be used to decide the question inasmuch as
the stimulus may act upon any of the numerous nerve fibres coursing among the muscle
fibers.
A muscle can be separated from all nerve influence by cutting the nerve which sup¬
plies it and waiting a sufficient length of time for degeneration of the nerve fibers to have
taken place. A complete physiological separation of nerve and muscle can be effected
more quickly by the use of the South American arrow-poison called "curara."
The following experiment will serve to illustrate the manner in which the site of action
of a drug can be determined; the preparation will be available also for establishing the in¬
dependence of the irritability of muscle from that of nerve as well as for studying the
comparative irritability of these two tissues.
Experiment.—Pith the brain of a frog, taking great care not to cause much bleeding.
If much bleeding occurs, pack the wound with a little cotton.
Slit the skin on the back of the left thigh above the position of the sciatic nerve.
Dissect the nerve carefully without injuring the femoral vessels. Raise the nerve with
a glass hook, and pass underneath it a narrow tape wet with normal saline. Bring the
ends of the tape to the front of the thigh, and tie firmly, about the middle, all of the
structures of the thigh with the exception of the sciatic nerve. By this means the left
leg below the ligature is excluded from the general blood supply, and this leg will be des¬
ignated hereafter as the unpoisoned limb. Wet a strip of filter paper with normal saline
and lay it over the nerve. Make a small opening with scissors in the skin of the upper
part of the back . This opening will lead into the dorsal lymph sac. Take a small tablet
of curara with forceps and push it through the opening into the dorsal lymph sac.
Dover the animal with bell jar and allow it to remain undisturbed for from twenty to
thirty minutes. At the end of this time the animal will be completely paralyzed with
the exception of the left leg.
Method of Determining the Site of Action of Curara.—(Suspend the frog by a hook
passed through the lower jaw and stimulate the skin of the foot of the poisoned leg
mechanically (pinch of forceps), or chemically (a drop of acetic acid), land observe what
follows. What inference can be made regarding the effect of curara on the structures
concerned in the observed phenomena? Construct a diagram showing the structures just
referred to and label it properly.
Connect the inductorium to the electric supply so as to obtain rapidly repeated in¬
duced currents. Connect the hand electrodes to the secondary coil.
45
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Dissect both sciatic nerves from the thigh to the vertebral column. Expose the gas-
trocenemius muscle of each leg by dividing and retracting the skin overlying the muscle.
Raise the right sciatic nerve with the glass hook and stimulate it with submaximal
induction shocks. Does the right gastracnemius contract? Stimulate the left sciatic in
the same manner and near the vertebral column, that is in a region supplied with curarized
blood. Does the left gastrocnemius contract? Has curara acted on the nerve fibers of
the nerve trunk?
Apply the stimulus to the right gastrocnemius directly. Does it respond?
Since the left nerve trunk responded to stimulation, though supplied at the stimulated
point with curarized blood, it is justifiable to infer that the right nerve trunk must
.have responded also; yet the right muscle did not contract. This muscle was supplied
with curarized blood, but the curara had evidently no effect upon the muscle since it re¬
sponded to direct stimulation. The site of action of curara must therefore be in some
structure located between the nerve fiber and the muscle fiber. What is this structure?
What are its histological features?
Is the irritability of a muscle independent of that of its nerve?
The Comparative Irritability of Nerve and Muscle.—There is a notable difference in
the irritability of nerve and muscle also shown by the effects of stimulation with induced
currents of definite strengths. This difference of irritability of nerve and muscle lends
support to the view which regards their irritability as independent.
The same curarwized frog may be used.d. Connect the inductorium for obtaining sin¬
gle induced currents. Apply the electrodes to the left sciatic nerve and find that position
of the secondary coil where the first (minimal) contraction of the related gastrocnemius
will be obtained on the break of the primary circuit. With the same strength of stimu¬
lus, stimulate the right gastrocnemius directly. Does it contract? What explanation can
be offered for this?
Again place the electrodes on the right gastrocnemius and move the secondary toward
the primary coil until the first evidence of a contraction is obtained on the break of the
primary circuit. With the same strength of stimulus, stimulate the left sciatic nerve
How does the contraction of the left gastrocnemius compare with that of the right just
observed ?
Which is the more irritable, nerve 01* muscle? Which is the more adequate stimulus
to a muscle, the nerve impulse or the induced electric current?
EXTENSIBILITY AND ELASTICITY.
Any object capable of increasing in length when pulled upon is said to be extensible;
if, on the cessation of the acting force the object regains its original length, such an ob¬
ject is said to be elastic. Muscle (striated and smooth) possesses the properties of exten¬
sibility and elasticity. These properties are shared by many other organic as well as in¬
organic substances.
In order to detect points of difference or of similarity the properties of extensibil¬
ity and elasticity should be studied in such lifeless substances as steel or rubber and then
in living muscle.
Extensibility and Elasticity of Rubber.—Mount the muscle lever 011 the adjustable
46
fo. -".11 4
-
'
-
'
■
stand and fasten the flat-jawed clamp a little above the lever. Clamp one end of a short
rubber band in the flat-jawed clamp; fasten the other end to the lever by means of the
muscle hook. Unscrew the after-loading screw. Bring the lever to the horizontal posi¬
tion. Adjust the writing point to the smoked surface of the paper and rotate the cylin¬
der by hand to obtain an abscissa. Carefully hang the scale pan (weight 10 grams) to the
lever. The rubber extends. Turn the cylinder by hand half a centimeter. Remove the
scale pan. Does the lever return to the abscissa? Is the elasticity of rubber perfect when
the force which extended it was slight?
Move the cylinder a centimeter. Replace the scale-pan. The rubber extends and
the lever descends. Move the cylinder half a centimeter. Carefully place a ten-gram
weight on the scale pan; the rubber extends again. Move the cylinder half a centimeter,
then add another ten-gram weight; following the extension of the rubber, move the cylin¬
der half a centimeter. Continue doing this u :itil from 80 to 100 grams are acting on the
rubber. Move the cylinder half a centimeter and remove the weights one by one, mov¬
ing the cylinder half a centimeter between each removal of a weight. Does the lever
return to the abscissa? If it does not, it indicates that the rubber is still extended de¬
spite the removal of the stretching force; this persisting extension is called the "exten¬
sion remainder." Is the extension remainder permanent?
How do the successive extensions of rubber compare with each other under the influ¬
ence of equal increments of weight? An imaginary line drawn through the extremity of
the successive ordinates is a straigth line. IIow does the curve of elasticity compare with
that of extensibility?
Extensibility and Elasticity of Muscle.—Prepare a gastrocnemius or a semimembrano-
sus-gracilis preparation with their bony attachments. Clamp one end in the flat-jawed
•elamp and connect the other end to the lever. Keep the preparation moist by the appli¬
cation with the camel's hair brush, of physiological salt solution. Repeat with the mus¬
cle the experiment just performed with the rubber band. Allow the same intervals of
time to elapse between each addition of a weight.
Is the elasticity of muscle perfect when the extending weight was slight? Is there
an "extension remainder" when a greater weight was used? Is it permanent? Is the ex¬
tension curve a straight line? The curved line obtained by joining the ends of the or¬
dinates approximates a "parabola." Evidently, the extension of muscle is not the same
for each increment of weight; the amount of extension decreases gradually with the suc¬
cessive addition of equal increments of weight, What form has the curve of elasticity?
Are the muscles in the body in a state of elastic tension? If so, what are the causes
of this tension? What function does the elasticity of muscle fulfill in the movements of
the body? What factors influence the extensibility and elasticity of muscle?
SMOOTH MUSCLE.
Smooth muscle is also called "plain," "non-striated," and "visceral" muscle. It
is found in the walls of hollow viscera such as the stomach, intestines, bronchi, ureter,
bladder, the arteries, veins, etc., and in other situations, as in the eyeball, where it enters
into the formation of the ciliary muscle and the muscles of the iris.
The Spontaneous Rhythmic Activity of Smooth Muscle.—Remove the stomach from a
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pithed frog. Cut two rings from the pyloric portion of the stomach. These rings should
be about 4 millimeters wide and are readily obtained by severing the stomach at right
angles to its long axis. Pull off the mucous membrane without crushing or in any way in¬
juring the muscle. Place the rings on the milk glass plate and cover them with filter paper
wet with physiological salt solution.
Mount the apparatus used in the study of the influence of temperature on the muscle
contraction. Connect one of the muscle rings with the hook of the L-shaped rod and the
lever. Counterpoise the lever with such a weight that the pull on the muscle ring will be
only half a gram. Immerse the muscle in a tall tumbler partly filled with Ringer's solu¬
tion.
Adjust the kymograph so as to obtain the slowest speed of the cylinder. Place the
writing point of the lever lightly against the smoked surface. Mount a signal magnet to
wTrite beneath the muscle lever and connect it to the time-marking circuit; the time record
should give five seconds intervals.. If the rhythmic contractions do not occur after ten or
fifteen minutes try the other ring. A number of rings should be tried until one is
found to be active. Describe the characteristics of the activity of the preparation. Do
all the contractions occur from the same abscissa, or are there variations in the height
from which the contractions begin? What is tone? How would (1) an increase in tone
manifest itself in the tracing? (2) a decrease in tone?
The Single Contraction of Smooth Muscle.—One of the rings which failed to give
rhythmic contractions may be used for this experiment. With the cylinder revolving at the
same speed, stimulate the muscle ring with a tetanizing current of moderate intensity for
about one second. How does the contraction of smooth muscle differ from that of
skeletal muscle? In order to estimate the length of the latent period, a signal magnet
should be placed in the primary circuit and made to write on the same perpendicular
line with the muscle lever. Another signal magnet in circuit with the electrical clock should
write beneath, giving a record of time at five seconds intervals.
CILIARY MOTION.
Certain epithelial cells lining some of the hollow organs of the body have their free
surface covered with hair-like processes called "cilia." These cilia are in constant mo¬
tion, and, though microscopic in size, are able to move relatively heavy bodies in a defi¬
nite direction with fair rapidity. Ciliary motion is a primitive form of contractile activity
and apparently is not dependent on any action of the nervous system. It is found in
many of the lower forms of animal life.
Experiments on Ciliary Motion—Pith a frog and pin it on the dissecting tray with
the back down. Cut away the ventral body wall and all viscera with the exception of
the esophagus and stomach. With the scissors split through the lower jaw, in the median
line and continue downward so as to open the entire esophagus lengthwise. Turn the sides
of the split lower jaw sideways and pin them down; spread the esophagus open and pin
the sides, in order that it may lie flat. The frog's esophagus is lined with ciliated epith¬
elium. The direction in which the cilia are waving may be demonstrated as follows:
Place a piece of cork or a clean piece of the frog's liver on the mucous membrane
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lining the roof of the mouth. Observe the motion of the cork or liver; what is the di¬
rection of the motion? Raise one end of the dissecting tray so that the cork must move
upward. Are the cilia able to carry the cork up the incline against the force of gravity?
The motion of the cilia depends on the irritability of the epithelial cells from which
they arise. Hence anything that affects the irritability of the cells will become manifest
in the behavior of the cilia. The two following experiments will illustrate these state¬
ments :
Place the dissecting tray flat on the table, and find out how long it will take for
the piece of cork to be moved from the roof of the mouth to the stomach end of the eso¬
phagus. Make three observations and take their average. Heat physiological salt solution
to 30° C., and using a pipette, bathe the mucous membrane freely with the warm solution.
Immediately, determine again the time required for the cork to be moved the same dis¬
tance. What effect has heat on the (activity of cilia?
Dip a piece of filter paper in ether, and holding it a short distance above the ciliated
surface, blow the ether vapor upon it. Wait a few seconds and determine again the time
occupied by the cork in moving the allotted distance. When the rate of movement has
returned to its normal figure, place the cork on the roof of the mouth and while it is
moving along the esophagus, blow ether vapor immediately ahead of it. What follows?
What effect has ether vapor on the activity of cilia?
THE EFFECTS OF THE GALVANIC CURRENT ON LIVING MATTER.
This subject will be discussed and demonstrated under the following outline:
Galvanotropism or Galvanotaxis.
Polarization.
Effects of the galvanic current on muscle:
(a) influence of the suddenness with which the current is 'applied.
(b) opening and closing contraction; galvanotonus.
(c) polar stimulation.
Effects of the galvanic current on nerve:
* (a)the development of a nerve impulse.
(b) the occurrence of electrotonic currents.
(c) electrotonic changes of irritability and conductivity.
(d) Pfluger's law of contraction.
Stimulation of human nerves:
(a) physical and physiological poles.
(b) monopolar method of stimulation.
(c) the "motor points."
(d) formula of contraction for man.
(e) reactions of degeneration.
44)
^ojui^xaTion o ,(3u^-3t^;r^k»
in studying the effect of the galvanic current upon nerves «in
llitu", it is necessary to confine the observations to stimulation at
but one elecrbrode afc a time, •Jo this method of stimulation the term
lax stimulation" is given (often oalled unipolar stimulation),
this method one electrode —• either anode or oathode — is placed
over Ihe nerve to be stimulated; this electrode is oalled the "Stimu¬
lating" electrode, 'The other electrode is placed over some indifferent
part of the body Such as the back of the neck or the sternum^ this elec¬
trode is called the "indifferent" electrode. The area of the skin
covered by the "stimulating" electrode must be relatively small, that
the current lines may be as dense as possible, short of Causing disoom^
fort to the patient, The area of the sJcin covered by the "Indifferentv
electrode must be relatively large to reduce the density of the current
lines and diminish the resistance to the passage of the current.
The T&© "stimulating" electrode is a nickel plated
rod terminating in a ball shaped end. The handle is of wood) it con¬
tains a brass core injro Which the electrode is screwed, at one end,
while the other end is hollowed for the reception of a wire. When in
uss, the ball shaped end must be covered with cotton tied securely and
saturated with salt solution,
She "indifferent" electrode consists of a brass disc, three
centimeters in diameter and covered with felt. This disc screws into
a handle similar to that of the stimulating; electrode, When in use,
the felt covered disc must be saturated salt solution.
The LocaliAOAJpf. ,1 Ms tor ppjir^t. As has been shown in
revious experiments', stimulation of a muscle through its nerve is
pre effective than direct stimulation* This is due to the greater
irritability of nerves as w**ll as to the distribution of the nerve im¬
pulses to all the muscle fibers, There are certain points over the
tody where the motor nerves can be most re-adily stimulated. These
points are Called " motor points " and coincide with the place of en—
imnoe of the nerve into the muscle, Charts have been made showing the
|p cat ion of the " motor points " for the surface of the entire body.
Consult a chart showing the flexor and extensor surfaces of the
(drm and locate the " motor points " shown as large dots. The induced
' cniirent is used for the purpose. If single shcohs are used the more
efficient pole of the secondary coil must lie connected with the stimul¬
ating elecrtr&dd, the indifferent electrode being connected with the
other pole, ( The more efficient-pole of the secondary is the one that
Is the cathode when the primary current is broken. Why? ) The rapidly
repeated induced current may also be used, TO reduce the resistance of
die epidermis it may &e necessary to moisten the skin thoroughly with
#7arm water. This can be done with a folded $owel soaked in warm Water
. ^ bound on the arm for a few minutes,
•
Connect the induotc&ium to obtain rapidly repeated induced cur¬
rents Connect the Indifferent eleotrode with cne of the poles of the
<3eoo^*rv coil and the stimulating eleotrode with the other, place the
(2)
9^e°trode on the back of the neck; start the Current and
ate the n motor points « With the stimulating electrode. Mark these
nts on the skin with an indelible pencil.
-?k§. 3^r9.nt_ ^ntroj.ler^ The galvanic current is supplied from a
>axy converter at an E.M.F. of 100 volts. This voltage is consider-
Ly in excess of that required. Ike current is therefore made to pass
rough a high resistance, consisting of a coil of fine wire srrund
wnd an insulated cylinder, a slider in contact with the coil can be
de to move its entire lengthy thus coming in oontaot gradually with
oessive turns of the wire. The left end of the coil is in eleotrloal
anection with binding—post No. 3; a mi111amperemeter is in series
ong the wire Joining this end of the coil to the binding-post, the
rouit being continued through binding-post No, 1. The slider is in
metrical connection with binding-post No, 3.
When the slider is at the &eft end of the coil, the E.M.F. is 0.
the slider is moved toward the right, the E.M.F. acting on the oir-
it between binding-posts 1 and 3 ( when these are connected ) gradu-
.ly rises, The voltage is indicated on the scale along which the
ider moves,
w^ti^thvanijC Current,
wmeot Dinding-pa^c No, "I ox the controller with one of the bind-p^sts
f a simple key. Run a wire from the other binding-post of the simple
ey to one of the middle binding-posts of a rooking key arranged to act
is a pole ohanger. Run another wire from binding-poet- No, 3 to the
Jther middle post of the rooking key. Attach wires to the two posts at
wis end of the rooking key. Connect the electrodes to the free ends of
these wires,
, Make the u stimulating 11 electrode the cathode; place it over
cue uln&r nerve or over any one of the motor points found previously.
Place the « indifferent » electrode over the back of the neck. The simr-
?le key being open, slide the oontaot of the controller to the mark in-
lioating lo volts. Make and then break the current. If no contraction
follows, elide the oontaot gradually, to increase the voltage about 6
Volts at a time, tasting between each rise in voltage until a contract-
Jen is obtained. When does She contraction occur, on opening or clos¬
ing the oirouit? The contractions should be clear out. Read the mill-
^-^flteter and note what current strength was needed to cause the contra¬
ction observed, Reverse the current so as to make the " stimulating
electrode the anode, Using the same current strength, close and then
open the circuit. There should be no Response if the current was Just
strong enough to cause a contraction on dosing the olrouit when the
Stimulating eleotrode was cathode. Increase the current strength grad—
pally, testing between each increase in voltage, until a contraction is
Obtained on closing the circuit. Read the milliammeter. (Continue in¬
creasing the ourrent strength gradually until a oontraction is obtained
On the opening of the circuit, and note the current strength on the
hilliammeter. Reverse the current and determine what strength of curi*
is nec-e-ssary toucans© a contraction on the opening of the circuit,
the » stimulating » 0Lectnod© _beingy^of .course ^. the_pathode,
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6 mA.
A.G.C.
7 mA.
A.O.C.
9 mA.
C.O.C,
12 mA.
Bring the contact of the controller back to zero and repeat thr
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trength necessary to cause responses on closing and opening the cir-
uit for either electrode, you are to observe the strength of the
trac t_ions with { 1 J weak, { 3 ) medium, and (3) strong
orrenTs. Tabulate the results and write an explanation of them bear—
ag in mind the facts previously discussed viz., that the stimulus on
losing occurs at the physiological cathodes, on opening at the phyftac
ological anodes, that cathodal stimulation is stronger than anodal,.
nd that the stimulus is stronger than anodal, and that the stimulus
s stronger the denser the current lines.
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REFLEX ACTION
By the term "reflex action," is meant, an involuntary action occurring in muscle or
gland tissue in response to the stimulation of afferent nerve fibers at the periphery.
The simplest mechanism necessary for a reflex action consists of at least the follow¬
ing structures:
(1) A receptive surface, e. g., skin, mucous membrane, special sense organ, etc.
(2) An afferent neurone.
(3) An efferent neurone.
(4) A responsive organ, e. g., skeletal muscle, smooth muscle (in the walls of a viscus,
blood vessel, etc.), or a gland.
The cells from which arise the efferent nerve fibers that are concerned in reflex
actions are found in the spinal cord, in the medulla, and in the mid-brain. A reflex
act may or may not be accompanied by sensation. W{iat is meant by a "conditioned" re¬
flex?
The most obvious, and therefore the most easily studied reflexes, are those occurring
in the skeletal muscles. They can be obtained most conveniently in a frog whose brain
has been destroyed by pithing, or removed 1 y decapitation.
Spinal Shock.—Before disturbing the frog, observe its attitude; note the position of
the limbs, the respiratory movements of the nostrils and flanks, the eyes, etc. Destroy
the brain by pithing as usual. Be sure that the medulla is destroyed by moving the pin
from side to side and slightly backward. Observe the posture of the frog immediately
after this operation and compare it with that of the normal animal. Suspend the animal
by passing a pin hook under the lower jaw and fastening the hook in the flat-jawed
clamp. Stimulate the toes of one foot with a rapidly repeated induced current. Is
there any result? Wiait a few minutes and repeat the stimulation. What is the result?
When a part of the spinal cord is severed from the rest of the. central nervous sys¬
tem, a notable depression of the functions of the cord follows. This depression is called
"spinal shock." It is much more accentuated in the part of the cord distal to the brain.
Spinal shock does not last very long in the frog, but in certain mammals it is very pro¬
found, and may last for a number of weeks.
Reflexes Resulting from Stimulation of Afferent Nerve-endings in the Skin—Reflex
contractions of muscles may be obtained by stimulating the afferent nerves in the skin,
by mechanical, chemical, and electrical methods of stimulation.
Mechanical Stimulation.—Pinch any toe of the right foot with forceps. What fol¬
lows? Was the movement on the side of stimulation? What muscles took part in the
movement? „.
Pinch a toe of the left foot. Describe what follows. Pinch a finger.
Pinch the whole foot very sharply. Are the movements which follow more extensive?
Are they confined to the side of the stimulation/
Reflexes occurring on the same side as that of the stimulation are called "unilateral"
reflexes. The site of stimulation determines what groups of muscles will respond. When
50
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the stimulus is weak few muscles come into play, and these are confined to muscles sup¬
plied with nerve fibers coming from that segment of the spinal cord related most directly
to the afferent neurones stimulated. When the stimulus is stronger a larger number of
muscles respond. This is due to the spreading of the afferent impulses to segments
of the cord higher up. The iafferent nerve impulses may cross to the opposite side of
the spinal cord and cause contractions of muscles on the opposite side. The muscles
concerned in this "crossed reflex" are symmetrical to those contracting on the side stim¬
ulated. The contractions on the side stimulated are, however, more intense than on the
opposite side.
These facts can be brought out more satisfactorily in the following experiments:
Chemical Stimulation.—Take a small glass beaker and fill it to a depth of about 3
centimeters with 0.2 per cent, sulphuric acid solution. Draw one leg aside, gently, with
.the glass rod. Immerse the tip of the toe of the other foot in the acid by raising the
beaker. After a few seconds, movements of the leg occur on the same side. Wash away
the acid by bathing the leg in a beaker of water.
Repeat this experiment on the other foot, and make notes of the results.
Dip the glass rod in the acid and touch a finger with it. Describe the result.
Repeat the experiments 011 the foot, with this difference, however,—that the whole
foot is immersed in the acid instead of the tip of the toe. Carefully note the results.
Wash away the acid between each experiment.
Electrical Stimulation.— (a) Single Induced Currents.—Connect the inductorium so as
to obtain single induced currents, placing a simple key in the primary circuit. Attach
thin wires to the binding posts of the secondary coil. Bend the ends of these wires and
push them into the skin of one foot. Place the secondary as far iaway as possible from
the primary coil; make and break the primary circuit and bring the secondary gradu¬
ally closer to the primary. Make and break the primary current iafter each advance of
the secondary coil. No reflex movements occur ;the single muscle twitch which is seen
when the stimulus is very strong is due to a direct stimulation of underlying muscles. Evi¬
dently a single stimulus, however strong, applied to afferent nerve endings is unable to
bring about reflex muscular contractions.
(b)Rapidly Repeated Induced Currents.—Connect the inductorium for obtaining tetan-
izing currents. Place the secondary well away from the primary coil and send tetanizing
shocks into the skin of the foot. If no effect follows, gradually push the secondary to¬
ward the primary until reflex contractions occur.
It appears from this experiment that the stimulus must be repeated with a sufficient
frequency before ia reflex movement can be obtained. This is due to a summation of
effects. The frequency with which the stimuli must follow each other to result in reflex
contractions of muscles may be shown by the next experiment.
Determination of the Number of Electric Stimuli per Second Necessary to Produce
Reflex Contractions.—Place the vibrating interrupter in the primary circuit of the induc¬
torium. Leave the secondary coil in the same position as in the preceding experiment.
Starting with five interruptions per second, try the effect of higher rates of stimulation.
Wait a few minutes between each increase in rate. Make a note of the number of stimuli
per second when the first reflex contraction was obtained.
51
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The Apparently Purposive Nature of Reflex Actions.—Put a few drops of acetic acid
(30 per cent.) in a watchglass and dip into it a small piece of filter paper about a half cen¬
timeter square. Be careful to see that the paper is merely moistened with the acid. With
forceps apply the square of filter paper to the inside of one thigh. Note the character
of the movements. Remove the paper, and immerse the frog in a beaker of water in order
to wash off the acid. Repeat this experiment after five minutes, but hold the foot se¬
curely to prevent the leg to which the acid is applied from moving. Does the other leg
move? What is the apparent purpose of its movements? Apply another square of paper
moistened with the acid as before, to other places, such as the skin of the chest, the skin
of the back near the tip of the urostyle, etc.
What explanation may be offered for the occurrence of these complex, co-ordinated,
and seemingly purposeful movements? Are they the result of a guiding intelligence, or
are they due merely to the action of a definite spinal mechanism?
Reflex Irritability.—The irritability of the structures taking part in a reflex action can
be estimated by determining the time that elapses from the moment of application of the
stimulus and the appearance of the muscle contraction. As this time varies with the
strength of the stimulus—being shorter with strong stimuli—it is necessary, for compara¬
tive purposes, to use ia stimulus of definite strength, such as a 0.2 per cent, solution of
sulphuric acid.
The length of time determined in this manner is distributed as follows: time for the
conduction of the nerve impulse from the endings of the afferent neurones to the ventral
horn of the spinal cord, possibly through one or several other neurones; time for the con¬
duction of the nerve impulse along the efferent neurone to the muscle; time of the latent
period of the muscle contraction. The true or reduced reflex time, however, is that re¬
quired for the transmission of the impulse within the spinal mechanism only. In speak¬
ing of reflex irritability, therefore, it is the irritability of the spinal mechanism which is
usually referred to.
Estimation of the Reflex Time on the Frog.—Immerse a definite portion of the foot
in 0.2 per cent, solution of sulphuric acid; count the number of seconds between the mo¬
ment of immersion and the movement of the leg. Wait at least three minutes, and re¬
peat this experiment. Do this five times with each leg at intervals of, at least, three min¬
utes. Take the average of the number of seconds for each leg. From these average fig¬
ures and other necessary data, calculate as accurately as possible, the true reflex time.
How does this time compare with the time consumed in the remainder of the reflex arc?
Influence of Strychnine on Reflex Irritability.—After obtaining the average reflex time
in a brainless frog, introduce a single drop of a 0.5 per cent, solution of strychnine sul¬
phate into the dorsal lymph sac.
In a few minutes test the reflex time. How does it compare with the average? Repeat
the test a few minutes later. Continue in the same way until the response follows so
rapidly upon the stimulation that the time cannot be estimated by such a simple method.
What effect has strychnine on reflex irritability?
goes on? Apply weak stimuli, such as a lif the response as absorption of the strychnine
What changes occur in the character oght touch to the skin in various parts of tie
52
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body. Describe the results. "What strength of stimulus was necessary in previous ex¬
periments to obtain a spreading of incoming nerve impulses to segments in the spinal
cord distant from the point of entrance of the afferent nerve? Are similar results ob¬
tained with much weaker stimuli under the influence of strychnine? What explanation
may be offered of the manner of action of strychnine? When the contractions become te¬
tanic, what group of muscles enters in violent contraction?
Pass the pithing needle into the spinal canal and destroy the spinal cord; can reflexes
still be obtained? Expose the sciatic nerve and gastrocnemius muscle. Stimulate them sep¬
arately with the induced current. What may be inferred concerning the action of strych¬
nine on the structures just stimulated?
Study of a Tendon Reflex in Man. The Knee-Jerk.—The so-called knee-jerk or pa¬
tellar tendon reflex is a quick forward thrust of the leg due to a brief contraction of the
quadriceps extensor muscles. To obtain this reflex the leg must be completely relaxed
and placed in such a position that the ligamentum patellae and quadriceps extensor will
be under slight tension; the ligamentum patellae is then struck a quick blow.
What explanations have been given to account for the knee-jerk? Which is likely to
be correct and why? Explain what is meant by "myotatic" irritability.
Apparatus.—The apparatus consists of (1) a freely swinging hammer provided with
a catch to hold it at any desired height ; this catch moves against a quadrant graduated
in degrees of the circle, (2) a padded support for the thigh, (3) a swing to hold the foot
and (4) a writing device to record the movements of the leg on the kymograph. This
apparatus is to be mounted on suitable stands.
Directians Preliminary to the Experiment.—In this experiment four students work
together, the first acting as subject, the second taking charge of the hammer and the ap¬
plication of the blows, the third looking after the application of the sensor and psychic
stimuli, and the fourth keeping full notes of the experiment and marking the kymo¬
graph record with numbers corresponding to similar numbers in his notes stating the char¬
acter and time of application of the various stimuli. The work should be done in a room
which is free from noises of any kind. This is a matter of importance as the success of
the experiment depends upon it. ie;:- t :' - ^
The subject lies on his left side, his head resting on a pillow, his right thigh supported
and his foot in the swing. The muscles should be fully relaxed and the lower leg must be
able to swing freely. The cord to which the swing is attached must hang vertically when
the leg is at rest. The back of the swing is connected by means of a thread with the
writing device, the point of which is carefully adjusted against the smoked paper. The
hammer must be so placed that the center of the striking face just comes in contact with
the skin over the middle of the patellar tendon when the hammer is hanging vertically,
the handle of the hammer being therefore, opposite the zero of the quadrant. The blow
is to be struck at right angles to the tendon. Ordinary clothing will not interfere with
the experiment. The subject must rest quietly iand with his eyes closed unless otherwise
directed. When all adjustments have been made the following experiments may be car¬
ried out.
(a) The Normal Knee-jerk.—The hammer is put on the catch previously placed at
10°, and then released. If the hammer tends to rebound, so that it would give a number
53
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Jzjpharaius VseJ ^-ev SrtoJijn^' He l\neadar\\,
body. Describe the results. "What strength of stimulus was necessary in previous ex¬
periments to obtain a spreading of incoming nerve impulses to segments in the spinal
cord distant from the point of entrance of the afferent nerve? Are similar results ob¬
tained with much weaker stimuli under the influence of strychnine? What explanation
may be offered of the manner of action of strychnine? When the contractions become te¬
tanic, what group of muscles enters in violent contraction?
Pass the pithing needle into the spinal canal and destroy the spinal cord; can reflexes
still be obtained? Expose the sciatic nerve and gastrocnemius muscle. Stimulate them sep¬
arately with the induced current. What may be inferred concerning the action of strych¬
nine on the structures just stimulated?
Study of a Tendon Reflex in Man. The Knee-Jerk.—The so-called knee-jerk or pa¬
tellar tendon reflex is a quick forward thrust of the leg due to a brief contraction of the
quadriceps extensor muscles. To obtain this reflex the leg must be completely relaxed
and placed in such a position that the ligamentum patellae and quadriceps extensor will
be under slight tension; the ligamentum patellae is then struck a quick blow.
What explanations have been given to account for the knee-jerk? Which is likely to
be correct and why? Explain what is meant by "myotatic" irritability.
Apparatus.—The apparatus consists of (1) a freely swinging hammer provided with
a catch to hold it at any desired height ; this catch moves against a quadrant graduated
in degrees of the circle, (2) a padded support for the thigh, (3) a swing to hold the foot
and (4) a writing device to record the movements of the leg on the kymograph. This
apparatus is to be mounted on suitable, stands.
Directians Preliminary to the Experiment.—In this experiment four students work
together, the first acting as subject, the second taking charge of the hammer and the ap¬
plication of the blows, the third looking after the application of the sensor and psychic
stimuli, and the fourth keeping full notes of the experiment and marking the kymo¬
graph record with numbers corresponding to similar numbers in his notes stating the char¬
acter .and time of application of the various stimuli. The work should be done in a room
which is free from noises of any kind. This is a matter of importance as the success of
the experiment depends upon it. r ^
The subject lies on his left side, his head resting on a pillow, his right thigh supported
and his foot in the swing. The muscles should be fully relaxed and the lower leg must be
able to swing freely. The cord to which the swing is attached must hang vertically when
the leg is at rest. The back of the swing is connected by means of a thread with the
writing device, the point of which is carefully adjusted against the smoked paper. The
hammer must be so placed that the center of the striking face just comes in contact with
the skin over the middle of the patellar tendon when the hammer is hanging vertically,
the handle of the hammer being therefore, opposite the zero of the quadrant. The blow
is to be struck at right angles to the tendon. Ordinary clothing will not interfere with
the experiment. The subject must rest quietly and with his eyes closed unless otherwise
directed. When all adjustments have been made the following experiments may be car¬
ried out.
(a) I he Normal Knee-jerk.—The hammer is put on the catch previously placed at
10°, and then released. If the hammer tends to rebound, so that it would give a number
........ . . . " ^ .
.
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■
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:
of blows, catch ft bpfote it strikes a second time. Find the position of the hammer where
the blow is followed by a movement of the leg of about two centimeters as shown on the
record. When this position is found, start the kymograph at a very slow speed (about
3 mm. per sec.) and record a series of about twenty normal knee-jerks, allowing the leg
to come to rest between the blows. Even under ideal conditions of absolute quiet, the
knee-jerk will be observed to vary in height. What does it indicate? With some sub¬
jects an increased tonus may at first be observed, with the result that the writing point
does not return to the base. This, however soon disappears as the subject becomes ac¬
customed to the experiment. Label the record.
(b) Psychic Reinforcement.—When the knee-jerks are of about uniform height, rec¬
ord a series of about ten normal jerks applying the blows rhythmically. Continue ap¬
plying the blows at the same rate and note the effect:
1. of speaking to the subject;
2. of giving him a problem in mental arithmetic, e. g. the multiplication of two
simple numbers;
3. of asking him to think of some stirring event, etc.
Note also the effect of any noise from the outside. Carefully label the record as ex¬
plained above.
(c) Motor Reinforcement.—After recording a series of ten or more jerks, and while
the blows >are being applied rhythmically, ask the subject to prepare to clench his fist
when told to do so. If a psychic reinforcement is noticed when the subject is spoken to.
give the order to clench the fist and do not release the hammer until just after the or¬
der has been given. Note whether the jerk is greater or less than the normal. Study
the effect of increasing and decreasing the time between the clenching of the fist and
the application of the blow.
What are the time limits within which (1) a reinforcement, (2) an inhibition, (3)
no change in the reflex are seen?
(d) Reinforcement by Sensor Stimuli.—After recording ten or more normal jerks,
study the effect of several sensor stimuli that are followed by reflex movements of vol¬
untary muscles, e. g. pulling the hair, tickling the face with a feather, producing an
unexpected sound, bringing a strong odor under the nostrils, or exciting the mucous mem¬
brane of the throat so as to produce voluntary or involuntary swallowing. Mark on the
smoked paper the time of application of each of these stimuli.
Explain how voluntary or reflex movements reinforce or inhibit the knee-jerk.
The student who acted ias subject receives the records of the experiment.
54
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CIRCULATION OF THE BLOOD
The blood circulates through a closed system of vessels which, collectively, constitute
the "vascular apparatus." The purpose of the circulation of blood is to supply the tis¬
sues of the body with the nutritive material and oxygen necessary for the maintenance
of their physiological activities and to remove from them the waste products which .are
among the results of such activities. Incidentally, the heat liberated in the active tissues
is distributed to all parts of the body. Since the exchange of materials takes place across
the wall of the capillaries, the main objects of the circulation are fulfilled while the
blood is flowing through these vessels. The arteries and veins, then, serve primarily, to
carry the blood to and from the capillaries.
The movement of the blood through the circulatory apparatus is due to the contrac¬
tions of a highly specialized part of it called, the heart. The student should carefully
review the anatomy of this organ.
THE HEART'S ACTION.
The Action of the Valves in the Mammalian Heart. (Gad's Ox-heart Experiment.)—
Demonstration. A brass cylinder capped with a round window is placed in the open
left auricle and another in the aorta of a large ox-heart. A tube attached to a rubber
bulb is inserted in the cavity of the left ventricle through its apex. The end of the tube
carries a small electric lamp to illuminate the interior of the ventricle and, through
the transparent valve leaflets, the interior of the auricle and aorta. Each cylinder has a
side tube connected by rubber tubing to a pressure bottle suspended above the heart.
The cylinder tied into the auricle is connected to a tube at the bottom of the bottle; the
cylinder tied into the aorta opens at the top of the bottle. Water is poured into the bot¬
tle until the entire system is filled and a moderate supply of water is left in the bottle.
Alternate compression and release of the rubber bulb will imitate the action of the ven¬
tricle; the action of the valves will be seen through the windows as the pressure of the
water rises and falls within the ventricle.
Make a sketch of the apparatus and describe the course of the water >and the action
of the valves during (1) the compression and (2) the release of the bulb.
Many of the important facts concerning the physiology of the heart were discovered
first through study of the frog's heart. These facts were shown later to be equally true
of the mammalian heart. For this reason, as well as for the sake of greater convenience,
the frog's heart may be used in the study of the essential characteristics of the heart's
contractions.
To Expose the Frog's Heart.—Pith the brain of a frog, carefully, so as to avoid bleed¬
ing. In the event of bleeding, pack the wound with a little cotton.
Place the frog, with its back down, pn the frog boiard; secure the limbs with pins
Make an incision through the skin in the median line, from the floor of the mouth to a
short distance beyond the caudal end of the sternum. Insert one blade of the scissors un¬
derneath the cephalic end of the sternum, and split the sternum longitudinally in the mid¬
dle, being careful to keep the lower blade close to the bone so as not to injure the heart
56
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beneath. Before reaching the end of the sternum, cut slightly to one side of the median
line in order to avoid severing the anterior abdominal vein. Draw the split sternum
apart by gentle, lateral traction on the forelimbs, and fasten these securely in their new
position. The heart will then be seen beating in the pericardium.
Pick up the pericardium carefully with fine forceps, and cut it from above down¬
ward, preferably while the heart is contracting. The following anatomical features of the
heart should be observed thorough^:
I. (a) Note the single ventricle, more or less conical in shape.
(b) The bulbus arteriosus, arising from the right side of the base of the ventri¬
cle and dividing above into the two aortae. ' ■ \
(c) The two auricles, which may be seen one on each side and beneath the bulbus.
(d) The auriculo-ventricular groove, seen between the auricles and ventricle.
(e) The points of interest on the dorsal aspect of the heart may be exposed to view
by tying a ligature around the very tip of the ventricle. The ventricle may then be raised
by gentle traction on the ligature. Note the sinus venosus—a narrow, triangular chamber
into which open the two superior venae cavae and the inferior vena cava. The line of
junction of the sinus with the right auricle indicated as a white crescentic line—the cres¬
cent or sino-auricular junction.
IT. Observe the beat of the heart.
(a) Count the number of beats per minute.
(b) What part of the heart is the first to contract? Note the sequence of the con¬
traction in all the parts just observed, viz.: ventricle, bulbus, auricles and sinus.
(c) Describe the change of shape of the different parts as they pass from the re¬
laxed to the contracted state.
(d) What change of color takes place during the action of any one part? What
explanation can be offered for this change of color?
(e) What is the character of the heart's action; do the contractions recur with
regularity? Does each phase of each beat seem to occupy the same length of time in each
succeeding contraction? What name is given to this property of the heart muscle?
(f) Does the contraction sweep unbroken from its starting point to its termina¬
tion, or are there places where the contraction is momentarily interrupted? Where are
these places and what explanation has been offered for this phenomenon?
The Heart is Automatic in its Action.—Raise the ventricle, and with sharp scissors,
cut wide of jdie sinus venosus, the veins which enter it. Hold the aortae with forceps and
cut them across. The heart can then be removed from the body. It is very important
not to injure the sinus venosus. Place the heart on a clean milk-glass plate and cover it
with a few drops of Ringer's solution.
Does the heart continue to beat? Are the contractions rhythmic? Does the heart de¬
pend on any action of the central nervous system for its contraction?
Count the number of beats per minute. Heat some Ringer's solution to 30° C. With
the pipette let some of the warm solution fall 011 the heart drop by drop. Count the num¬
ber of beats in a full minute while the warm solution is dropping on the heart. Re¬
peat the same experiment with Ringer's solution cooled to 10° C. ? ^
What influence has (a) heat, (b) cold, on the activity of the isolated heart?
Rhythmicity of Various Parts of the Heart.—Count the number of beats per minute
56
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of an isolated heart at room temperature. Separate the sinus from the right auricle by
cutting at the sino-auricular junction. Wait a few moments for any possible effect of the
operation to pass off. Does the sinus go on beating? What is the rate of its beat? Do
the auricles and ventricles beat? If so, what is the rate of their beat?
Separate the auricles from the ventricle by cutting immediately above the auriculo-
ventricular groove. Again wait a few moments. Do the auricles beat? If so, what is
the rate of their beat? Does the ventricle beat? If so, make a note of the rate of its con¬
tractions.
Cut transversely through the ventricle just below the auriculo-ventricular groove
Does the apical portion of the ventricle beat spontaneously? Apply a gentle mechanical
stimulus to it, such as touching with the point of the forceps. What is the result? Ap¬
ply a chemical stimulus by laying on it a crystal of sodium chloride. What is the result?
How does this result differ from that obtained by mechanical stimulation. Are the va¬
rious parts of the heart irritable? How do they show their irritability? Which part of
the heart is most highly rhythmic? Which parts have the property of automatic activ¬
ity most highly developed?
Study of the Heart-beat by the Graphic Method.—Pith a frog. If there is much bleed¬
ing pack the wound with cotton. Fasten the frog on the frog board. Expose the heart
freely; divide a band of connective tissue seen back of the ventricle; this is the frenum
and it carries a small vein which may be ligated by tying the frenum before cutting.
Support the ventricle with the finger tip and insert a sharp hook, or place a pincette
near the ventricular apex. Mount the frog board on the adjustable stand. Fasten the bal¬
ance lever to the same stand. Pass a fine wire hook into the pin hole nearest the axis
on the short arm of the lever. Pass the free end of the heart-hook, or of the pincette into
the eye of the lever-hook. Carefully adjust the lever until it is horizontal during the time
that the heart is relaxed. Bring the writing point of the lever delicately in contact with
the smoked paper on the kymograph. Incline the kymograph in such a way as to insure a
uniform degree of pressure of the writing point during all its movements. A levelling ta¬
ble may be necessary. The record should be taken at a moderate speed of the cylinder.
To determine the rate of the heart beat, it is necessary to record, simultaneously,
equal intervals of time. Arrange the electromagnetic signal to write immediately below
the heart lever. Connect it with the time-marking circuit. The electrical clock has been
set to give five seconds intervals.
Identify the various events of the heart's action with the movements of the lever and
the record traced by the writing point. The tracing of any one beat may show three,
more often only two, elevations separated from each other by slight depressions. What
are the elevations due to? What is the significance of the depressions? When the ven¬
tricle contains much blood the curve of its contraction is more or less oblique near the
apex; if bleeding has occurred the lever rises vertically and the apex of the curve may
be rather sharp. What explanation can be offered for these observations?
The Influence of Temperature on the Heart's Action.—Note the temperature of the
room in which the experiment just described was performed. Cool some Ringer's solution
to 10° C. While a record of the heart's action is being taken, let the cold solution drop
steadily on the heart from a fine pipette. Observe the result.
57
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of an isolated heart at room temperature. Separate the sinus from the right auricle
cutting at the sino-auricular junction. Wait a few moments for any possible effect of
operation to pass off. Does the sinus go on beating? What is the rate of its beat? L
the auricles and ventricles beat? If so, what is the rate of their beat?
Separate the auricles from the ventricle by cutting immediately above the auriculo-
ventrieular groove. Again wait a few moments. Do the auricles beat? If so, what is
the rate of their beat? Does the ventricle beat? If so, make a note of the rate of its con¬
tractions.
Cut transversely through the ventricle just below the auriculo-ventrieular groove
Does the apical portion of the ventricle beat spontaneously? Apply a gentle mechanical
stimulus to it, such as touching with the point of the forceps. What is the result? Ap¬
ply a chemical stimulus by laying on it a crystal of sodium chloride. What is the result?
How does this result differ from that obtained by mechanical stimulation. Are the va¬
rious parts of the heart irritable? How do they show their irritability? Which part of
the heart is most highly rhythmic? Which parts have the property of automatic activ¬
ity most highly developed?
Study of the Heart-beat by the Graphic Method.—Pith a frog. If there is much bleed¬
ing pack the wound with cotton. Fasten the frog on the frog board. Expose the heart
freely; divide a band of connective tissue seen back of the ventricle; this is the frenum
and it carries a small vein which may be ligated by tying the frenum before cutting.
Support the ventricle with the finger tip and insert a sharp hook, or place a pincette
near the ventricular apex. Mount the frog board on the adjustable stand. Fasten the bal¬
ance lever to the same stand. Pass a fine wire hook into the pin hole nearest the axis
on the short arm of the lever. Pass the free end of the heart-hook, or of the pincette into
the eye of the lever-hook. Carefully adjust the lever until it is horizontal during the time
that the heart is relaxed. Bring the writing point of the lever delicately in contact with
the smoked paper on the kymograph. Incline the kymograph in such a way as to insure a
uniform degree of pressure of the writing point during all its movements. A levelling ta¬
ble may be necessary. The record should be taken at a moderate speed of the cylinder.
To determine the rate of the heart beat, it is necessary to record, simultaneously,
equal intervals of time. Arrange the electromagnetic signal to write immediately below
the heart lever. Connect it with the time-marking circuit. The electrical clock has been
set to give five seconds intervals.
Identify the various events of the heart's action with the movements of the lever and
the record traced by the writing point. The tracing of any one beat may show three,
more often only two, elevations separated from each other by slight depressions. What
are the elevations due to? What is the significance of the depressions? When the ven¬
tricle contains much blood the curve of its contraction is more or less oblique near the
apex; if bleeding has occurred the lever rises vertically and the apex of the curve may
be rather sharp. What explanation can be offered for these observations?
The Influence of Temperature on the Heart's Action.—Note the temperature of the
room in which the experiment just described was performed. Cool some Ringer's solution
to 10° C. While a record of the heart's action is being taken, let the cold solution drop
steadily on the heart from a fine pipette. Observe the result,
57
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Heat some Ringer's solution to 30° C. When the heart has returned to its former
rate, drop the warm solution on the heart in the same manner as the cold solution.
What effects has a low temperature on the heart's action? A moderately high tem¬
perature? Describe these effects in detail.
The Irritability of the Heart.—The heartmuscle, in common with all other forms of
living matter, possesses irritability. The heart shows that it is irritable by responding to
the application of a stimulus in that it converts potential into kinetic energy. The ki¬
netic energy takes the following forms: mechanical motion, heat and electricity.
Whatever be the nature of the physiological stimulus, it must of necessity, arise within
the heart, since this organ continues to exhibit its characteristic activities after complete
isolation from the body—provided the proper conditions are maintained. The heart mus¬
cle will respond also to artificial stimulation—mechanical, chemical, electric and thermic
—just as other kinds of muscle tissue.
In order to demonstrate the effects of artificial stimulation it is necessary, first, to
abolish the action of the physiological stimulus, and thus, to bring the heart to a com¬
plete standstill. This can be accomplished by means of the first Stannius ligature.
The Stannius Ligature.—Pith a frog, fasten it on the frog board, and expose the heart
freely, as in the previous experiments. With an aneurism needle, pass a thread under
the two aortae, and guide it in such a way as to make it slip beneath the auricles. Raise
the ventricle; cut the frenum, and tie the thread exactly over the junction of the sinus
and the auricle. What follows the tying of the ligature? If the ligature is not placed
properly no effect will follow its tying. Leave the ends of the ligature long.
The Effect of a Gradual Increase in the Strength of the Stimulus on the Heart's Con¬
tractions.—Having brought the auricles and ventricle of the frog's heart to a standstill, re¬
move the heart from the body with sharp scissors. Mount the heart for electric stimu¬
lation on the "apparatus which was used in the study of the .effect of temperature on
muscle. Pass the hook of the L-shaped rod through the heart immediately above the liga¬
ture; the free ends of the ligature may be brought around the hook and tied. Insert
the hook at the end of the fine copper wire coming from the insulated binding post into
the apex of the ventricle. Connect the heart by means of the thread and hook at¬
tached to the fine copper Wire, with the balanced lever. It may be advantageous
to counterpoise the lever slightly in order to avoid undue pull on the heart. Arrange
the inductorium for single induction shocks with a simple key in the primary circuit;
connect the secondary coil with the L-shaped rod and the insulated binding-post.
Find that position of the secondary coil where the weakest break stimulus will make
the heart contract. Record the contraction on the stationary cylinder. Turn the cylinder
a few millimeters. Move the secondary a short distance toward the primary. Wait one
minute, then stimulate the heart with a break shock. Repeat these manipulations a num¬
ber of times until the heart is receiving a stimulus of maximal strength. Wait one min¬
ute betwen each stimulation. Do the heart's contractions vary in height under the in¬
fluence of stimuli of different strengths? How does the heart muscle differ in this respect
from the skeletal muscle? What is meant by the "all-or-none" law? Why was it neces¬
sary to wait a relatively long time between each stimulation? The effect of stimulation
58
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repeated at short intervals, can be studied with the same preparation after the heart has
been allowed to rest.
Staircase Contractions.—Stimulate the heart with a weak break shock at intervals of
five seconds. Record each contraction on the stationary cylinder, a few millimeters apart,
or on a cylinder moving at a very slow speed.
What is the effect of stimulation of the heart at relatively short intervals? What ex¬
planation can be offered for this phenomenon? How can this "staircase" effect be recoil
ciled with the "all-or-none" law?
The Changes of Irritability Which Occur During the Cycle.—Pith a frog, expose the
heart in the usual manner. Mount on the adjustable stand the frog board, the insulated
binding post provided with a fine copper wire, and the balance lever, one above the other
in the order named. Connect the apex of the ventricle with the lever as explained above.
Pass the hook at the end of the fine copper wire through the wall of the base of the ven¬
tricle. Connect the secondary coil of the inductorium with the lever and the insulated
binding-post. Arrange the inductorium for single induction shocks, placing a signal
magnet and the simple key in the primary circuit. See that the signal magnet writes on
the same vertical line with the heart lever, and as close to it as convenient. Mount
another signal magnet to write beneath, and connect it with the time circuit.
Stimulate the ventricle with weak break shocks, being careful to short circuit the sec¬
ondary before making the primary. Send the stimulus into the ventricle at various times
in the systole aricl diastole. The cylinder should be moving at a moderately fast speed,
so as to bring out the record of auricular and ventricular contractions distinctly. Draw
ordinates joining the moment of stimulation, as shown by the signal magnet, with the rec¬
ord of the heart's action above.
What followed the application of the stimulus during the systole of the ventricle?
What was the result of stimulation during diastole?
What is meant by the term "refractory?" During what phase of the heart's action
was the heart refractory to stimulation? What explanation is given for the "refractory
period" of the heart? What relationship did your experiment show between the height
of the "extra-systole" and its position in the diastole? What inference can you make re¬
garding the progress of return of the irritability? Note the pause which follows the
extra-systole. Is the pause longer than the average? Why was the name "compensato
ry" given to this pause? What is the true explanation for its occurrence? Use your trac¬
ings as part evidence of this explanation.
The Influence of Inorganic Salts on tho Heart's Action.—In seeking for the cause of
the heart beat, systematic investigations of the influence of the various constituents of
the blood on the heart's action have been undertaken. Among the most fruitful of these
investigations, must be mentioned the study of the influence of the various inorganic
salts found in the blood.
The following experiments will illustrate the influence of Na, Ca and K salts on the
heart muscle:
Remove a ring of muscle three milimeters wide from the apex of the ventricle of the
tortoise by making two cuts, transversely to the long axis of the ventricle. Divide the ring
so obtained at one point. Attach one end of the strip to the L-shaped rod and the other
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tions of the heart are recorded on a Hurthle kymograph. The remainder of the experi¬
ment and other details will be explained during the demonstration.
THE CARDIAC NERVES.
It has been shown that the heart can be removed from the body and that under such
circumstances it will continue to beat rhythmically provided the proper conditions are
present. In other words, the cause of the heart beat resides in the organ itself: the
heart is automatic in its action.
The heart, however, is connected with the central nervous system by two sets of nerves
whose function is to carry nerve impulses which regulate the rate and force of the;
heart's contractions in accordance with the needs of the body. These nerves are the vagus
and the sympathetic. These two nerves are separate in mammals, but in the frog and oth¬
er animals they are enclosed in the common sheath of the vagus for a considerable part
Nerve of the Frog. Ventral View. (G. Bach-
marm.) g. p. n., glossopharyngeal nerve; p. h. m.,
petro-hyoid muscles; c.a., cutaneous artery; v.n.,
vago-sympathetic nerve; i.j.v., internal jugular
vein; b. n., brachial (2nd spinal) nerve; h.g.n.,
hypoglossal nerve; gl., glottis; l.n., laryngeal
nerve; I. a., left auricle; c.b.v., cardiac branch of
vago-sympathetic nerve; v. a., right auricle; cr.,
crescent; s. v., sinus venosus.
Dissection of the Vago-sympathetic Nerve of the Frog.—Pith a frog and expose the
heart, but leave the pericardium intact until the dissection is completed. Draw the right
foreleg laterally and separate it from th? trunk, together with the scapula.
61
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Push a small test tube into the esophagus so as to stretch the tissues between the an¬
gle of the jaw and the median line. A number of nerves are then readily seen running
from the angle of the jaw transversely toward the median line. Two of these, viz., the
glossopharyngeal and the hypoglossal, turn forward toward the floor of the mouth. Two
other nerves run close to the cutaneous artery; the one on the caudal side of the artery is
the vago-sympathetie, the other is the laryngeal branch of the vagus. Immediately above
and parallel to these nerves and the artery is a group of slender muscles, the petro-hyoid
muscles. Identify these structures with the aid of the diagram (Fig. 3.)
Tie a ligature around the vago-sympathetic as close to its point of exit as possible.
Divide the nerve on the central side of the ligature and dissect it free for a little dis¬
tance toward the heart. Moisten the nerve with physiological salt solution. Divide the
other three nerves anywhere along their course. Remove the test tube.
The Effect on the Heart of Stimulating the Vago-sympathetic.—Divide the pericar¬
dium, and connect the heart by means of hooks to the heart-lever. Make sure that
the frog is securely fastened to the board. Arrange the inductorium for rapidly repeated
induced currents with the simple key and the electro-magnetic signal in the primary circuit.
Let the signal write a short distance beneath the heart lever and on the same perpendicu¬
lar line.
Start the drum at moderate speed and record a series of beats. Place the nerve on
the hand electrodes and close the key in the primary. The secondary should be well out
so as to produce weak currents. Let the drum revolve until the heart has fully recov¬
ered. Repeat the same procedure using this time a stronger current. Test the effect of
short and of prolonged stimulation.
Examine the tracings. Is there any latent period? What is its length expressed in
terms of heart beats? In what phase of the cycle is the heart stopped? Is there any
change in the tone of the heart during stimulation? Is the effect continued after stimu¬
lation has ceased? Describe the manner in which the heart recovers; observe the height
of the succeeding contractions, the rate as compared with that preceding stimulation; the
auriculo-ventricular conduction as shown by the position of the auricular contraction in
reference to the succeeding ventricular contraction. Compare the results obtained with
weak and strong stimulation and describe the influence of the duration of stimulation.
Stimulation of the Crescent.—Record a series of contractions. While the record con¬
tinues place the electrodes carefully in contact with the crescent—the white line at the
sino-auricular junction. Stimulate first with a weak interrupted current, and later
when the heart has fully recovered, with a strong current.
Drugs Acting on the Intracardiac Inhibitor Mechanism.
The Effect of (a) Nicotine. We have seen that the heart can be inhibited by stimu¬
lating the vagus fibers in the vago-sympathetic trunk and by stimulating the crescent.
The effect of stimulation of the crescent might be the result of the stimulation of the va¬
gus fibers, or of another set of neurones located between the terminals of the vagus fibers
and the heart muscle. The neurone in the vagus proper could therefore be compared to
a preganglionic neurone, while the neurone in the wall of the heart would represent a
postganglionic neurone.
It has been shown by Langley that when a sympathetic ganglion is painted with nico¬
tine, the nerve impulses carried by the preganglionic nerve fibers are blocked at the syn¬
apse between the terminals of these fibers and the nerve cells which give origin to the post¬
ganglionic nerve fibers. Nicotine may therefore be used to solve the question as to the
manner in which the vagus nerve fibers are connected with the heart, whether direct-
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Push a small test tube into the esophagus so as to stretch the tissues between the an¬
gle of the jaw and the median line. A number of nerves are then readily seen running
from the angle of the jaw transversely toward the median line. Two of these, viz., the
glossopharyngeal and the hypoglossal, turn forward toward the floor of the mouth. Two
other nerves run close to the cutaneous artery; the one on the caudal side of the artery is
the vago-sympathetic, the other is the laryngeal branch of the vagus. Immediately above
and parallel to these nerves and the artery is a group of slender muscles, the petro-hyoid
muscles. Identify these structures with the aid of the diagram (Fig. 3.)
Tie a ligature around the vago-sympathetic as close to its point of exit as possible.
Divide the nerve on the central side of the ligature and dissect it free for a little dis¬
tance toward the heart. Moisten the nerve with physiological salt solution. Divide the
other three nerves anywhere along their course. Remove the test tube.
The Effect on the Heart of Stimulating the Vago-sympathetic.—Divide the pericar¬
dium, and connect the heart by means of hooks to the heart-lever. Make sure that
the frog is securely fastened to the board. Arrange the inductorium for rapidly repeated
induced currents with the simple key and the electro-magnetic signal in the primary circuit.
Let the signal write a short distance beneath the heart lever and on the same perpendicu¬
lar line.
Start the drum at moderate speed and record a series of beats. Place the nerve on
the hand electrodes and close the key in the primary. The secondary should be well out
so as to produce weak currents. Let the drum revolve until the heart has fully recov¬
ered. Repeat the same procedure using this time a stronger current. Test the effect of
short and of prolonged stimulation.
Examine the tracings. Is there any latent period? What is its length expressed in
terms of heart beats? In what phase of the cycle is the heart stopped? Is there any
change in the tone of the heart during stimulation? Is the effect continued after stimu¬
lation has ceased? Describe the manner in which the heart recovers; observe the height
of the succeeding contractions, the rate as compared with that preceding stimulation; the
auriculo-ventricular conduction as shown by the position of the auricular contraction in
reference to the succeeding ventricular contraction. Compare the results obtained with
weak and strong stimulation and describe the influence of the duration of stimulation.
Stimulation of the Orescent.—Record a series of contractions. While the record con¬
tinues place the electrodes carefully in contact with the crescent—the white line at the
sino-auricular junction. Stimulate first wi th a weak interrupted current, and later
when the heart has fully recovered, with a strong current.
Drugs Acting on the Intracardiac Inhibitor Mechanism.
The Effect of (a) Nicotine. We have seen that the heart can be inhibited by stimu¬
lating the vagus fibers in the vago-sympathetic trunk and by stimulating the crescent.
The effect of stimulation of the crescent might be the result of the stimulation of the va¬
gus fibers, or of another set of neurones located between the terminals of the vagus fibers
and the heart muscle. ^The neurone in the vagus proper could therefore be compared to
a preganglionic neurone, while the neurone in the wall of the heart would represent a
postganglionic neurone.
It has been shown by Langley that when a sympathetic ganglion is painted with nico¬
tine, the nerve impulses carried by the preganglionic nerve fibers are blocked at the syn¬
apse between the terminals of these fibers and the nerve cells which give origin to the post¬
ganglionic nerve fibers. Nicotine may therefore be used to solve the question as to the
manner in which the vagus nerve fibers are connected with the heart, whether direct-
62
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Push a small test tube into the esophagus so as to stretch the tissues between the an¬
gle of the jaw and the median line. A number of nerves are then readily seen running
from the angle of the jaw transversely toward the median line. Two of these, viz., the
glossopharyngeal and the hypoglossal, turn forward toward the floor of the mouth. Two
other nerves run close to the cutaneous artery; the one on the caudal side of the artery is
the vago-sympathetic, the other is the laryngeal branch of the vagus. Immediately above
and parallel to these nerves and the artery is a group of slender muscles, the petro-hyoid
muscles. Identify these structures with the aid of the diagram (Fig. 3.)
Tie a ligature around the vago-sympathetic as close to its point of exit as possible.
Divide the nerve on the central side of the ligature and dissect it free for a little dis¬
tance toward the heart. Moisten the nerve with physiological salt solution. Divide the
other three nerves anywhere along their course. Remove the test tube.
The Effect on the Heart of Stimulating the Vago-sympathetic.—Divide the pericar¬
dium, and connect the heart by means of hooks to the heart-lever. Make sure that
the frog is securely fastened to the board. Arrange the inductorium for rapidly repeated
induced currents with the simple key and the electro-magnetic signal in the primary circuit.
Let the signal write a short distance beneath the heart lever and on the same perpendicu¬
lar line.
iStart the drum at moderate speed and record a series of beats. Place the nerve on
the hand electrodes and close the key in the primary. The secondary should be well out
so as to produce weak currents. Let the drum revolve until the heart has fully recov¬
ered. Repeat the same procedure using this time a stronger current. Test the effect of
short and of prolonged stimulation.
Examine the tracings. Is there any latent period? What is its length expressed in
terms of heart beats? In what phase of the cycle is the heart stopped? Is there any
change in the tone of the heart during stimulation? Is the effect continued after stimu¬
lation has ceased? Describe the manner in which the heart recovers; observe the height
of the succeeding contractions, the rate as compared with that preceding stimulation; the
auriculo-ventricular conduction as shown by the position of the auricular contraction in
reference to the succeeding ventricular contraction. Compare the results obtained with
weak and strong stimulation and describe the influence of the duration of stimulation.
Stimulation of the Crescent.—Record a series of contractions. While the record con¬
tinues place the electrodes carefully in contact with the crescent—the white line at the
sino-auricular junction. Stimulate first wi th a weak interrupted current, and later
when the heart has fully recovered, with a strong current.
Drugs Acting on the Intracardiac Inhibitor Mechanism.
The Effect of (a) Nicotine. We have seen that the heart can be inhibited by stimu¬
lating the vagus fibers in the vago-sympathetic trunk and by stimulating the crescent.
The effect of stimulation of the crescent might be the result of the stimulation of the va¬
gus fibers, or of another set of neurones located between the terminals of the vagus fibers
and the heart muscle. ^The neurone in the vagus proper could therefore be compared to
a preganglionic neurone, while the neurone in the wall of the heart would represent a
postganglionic neurone.
It has been shown by Langley that when a sympathetic ganglion is painted with nico¬
tine, the nerve impulses carried by the preganglionic nerve fibers are blocked at the syn¬
apse between the terminals of these fibers and the nerve cells which give origin to the post¬
ganglionic nerve fibers. Nicotine may therefore be used to solve the question as to the
manner in which the vagus nerve fibers are connected with the heart, whether direct-
62
TJfcJCIJVG 03T EFFECT O?ST TI\Ui>()TlNC, CHSSCEN"T
;
-
.
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. < • ■ • »■ d
-Hi «i iimij (} ni ^oiT l»«>i{ti»} « rii m<>d aiij ^Xjz/l .h»E <Nft Jo iioividjrtal xallt^i
llama afloiafom sui t>! . tluo . ->rit q -•? .'wswoil ,u«.n svviq
ui nib lit o mdl o — -'ji - litatu i •*>* i* ►qjs ?lc
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ly with the muscle fibers or indirectly through the intermediation of another neurone.
It ind that strength of interrupted currents that will produce complete inhibition of
the heart when applied to the vago-sympathetic nerve. Paint the heart with a camel's
hair brush dipped in 0.2 per cent, solution of nicotine. In from three to five minutes stim¬
ulate the vagus nerve again. If the heart is inhibited, paint the heart again with nico¬
tine ; wait a few minutes, then stimulate the vagus. If the heart does not stop, apply the
stimulation to the crescent. What follows? What inference can you make regarding the
mode of termination of the vagus nerve fibers? Do they go directly to the heart mus¬
cle, or do they terminate around the cells of another neurone?
(b) Pilocarpine. Wash the heart of the frog just used with physiological salt solution
and proceed with this and the next experiment. If the heart is not in good condition,
prepare another frog.
Paint the heart with a 1 per cent, solution of pilocarpine by means of a clean camel's
hair brush. Describe the effect of the drug on the frequency and height of the heart's
contractions and on the tone of the heart muscle.
(c) Atropine. Wash the heart with physiological salt solution and apply 0.5 per cent,
solution of atropine sulphate. Describe the effect of atropine.
Stimulate the vago-sympathetic nerve. Is the heart inhibited? Apply the stimulation
to the crescent. Is there any inhibition of the heart? Atropine suspends the conductiv¬
ity of postganglionic fibers.
Reflex Inhibition of the Heart.—Expose the heart in a pithed frog in the usual man¬
ner. Take the precaution, however, to pith the cerebrum only, to make incisions as small
as convenient and to handle the tissues gently.
Place the stomach or a loop of intestines on a glass plate. Observe the frequency of
the heart beats. Strike the stomach or intestine a sharp blow by the sudden release of
a bent whale bone; the handle of a scalpel may be used.
Note what follows. Repeat the experiment until successful. There should occur an in¬
hibition of the heart varying in degree from a mere slowing to complete arrest in di¬
astole. Destroy the remainder of the central nervous system with the pithing needle. Re¬
peat the experiment. Is there any inhibition of the heart? Explain.
The Action of the Vagi in the Mammal. (Demonstration.) A dog is given a hypo¬
dermic injection of morphine. In about half an hour it is etherized, the vagus nerves are
exposed and ligatures passed under them. A tracheal cannula is tied in position; the chest
is opened under artificial respiration and the heart is seen beating in the pericardium. The
phrenic nerves are cut. The pericardium is slit open and its edges are stitched to the
side of the thoracic wound. The right auricular appendage and the right ventricle are
connected by means of hooks and threads to separate tambours and these communicate
through rubber tubes with recording tambours. The levers write on the smoked paper of
the Hurthle kymograph, together with a signal magnet and a time marker.
Note the frequency and height of the auricular and ventricular beats; note their se¬
quence. What is the conduction time? The two vagi are cut one after the other, in
quick succession; the key in connection with the signal magnet is closed and opened at
each cutting. What changes occur in the heart's action? What inference can be drawn
regarding the normal degree of activity of the cardio-inhibitor center?
The peripheral end of each vagus is st imulated with rapidly repeated induced cur¬
rents, first of low intensity and then of greater intensity. Note the effect. Very often
63
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.
.nh'j.-r?,- h«o-; > tj il li i twi/i 0 ' p.. -fir . V. Vt* i
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m
there is a notable difference in the action of the right and left nerves. These differences
will be discussed as they occur.
The receiving tambours are removed. Feel the heart as it beats; describe the impres¬
sion it gives, particularly as regards the vigor of its contractions. What change of con¬
sistency occurs when the vagus is stimulated with a maximal interrupted current? Note
the change in size and color.
THE VASCULAR APPARATUS.
The vascular apparatus consists of a closed system of vessels through which the blood
flows to and from the heart. The blood is kept in motion in this system through the
pumping action of the heart aided and modified by other forces. Two main phenomena
may be observed in the vascular apparatus, viz., velocity and pressure. These phenomena
differ more or less typically in the three parts of the vascular apparatus—arteries, capil¬
laries, veins.
The student should familiarize himself with those facts of hydrodynamics which will
be of value in elucidating the phenomena of velocity and pressure that occur in the vas¬
cular system.
Some of the characteristics of the blood flow in various parts of the vascular appa¬
ratus can be observed in the frog's mesentery.
The Circulation as Seen in the Mesentery of the Frog\—Pith a frog and pack the
wound with cotton to stop any bleeding. Place the frog on its back on a cork board es¬
pecially provided for this purpose. Pin the limbs securely to the board. Cut through
the abdominal wall on the side near the small stage. Gently pull out a loop of small in¬
testine and arrange it so that the mesentery will overlie the stage. The loop can be se¬
cured in position by means of pins which can be pushed into small holes in the side of
the stage. Do not stretch the mesentery. See that it lies evenly. Put a few drops of phy¬
siological salt solution on the mesentery. Arrange the board on the stage of the microscope
and examine the mesenteric blood vessels with a low power objective.
Choose a field which does not contain too many blood vessels. Observe the character
of the blood flow. In some vessels the flow is remittent, i. e., wThile the flow never ceases
it undergoes alternate acceleration and retardation. In what kind of vessel is this flow ob¬
served? What is the direction of the flow, toward or away from the intestine? Note that
in another set of large vessels the flow is steady and continuous. What are these vessels?
What is the direction of the flow in these vessels in reference to the intestine? Note the
very fine vessels in which blood corpuscles usually pass singly. What are these vessels?
What is the character of the flow in them? -Compare the velocity of the blood in the
three kinds of vessels mentioned, so far as can be judged by the eye. In which vessels is
the velocity least? Why is this the case? Of what advantage is it that the blood should
move more slowly in these vessels?
Examine one of the larger vessels (artery or vein) with a high power objective. Note
the speed of the blood from the periphery to the axis of the stream by observing the pas¬
sage of the blood corpuscles. Is there any difference in the speed of the blood at the
periphery and at the axis of the stream?
The same preparation can be used for the study of the process of inflammation.
This can be brought about by touching the mesentery with a glass rod drawn to a point
and which has been dipped in tincture of cantharides or some other irritant. Among the
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phenomena which may be observed, the passage of the white blood cells across the wall
of the blood vessels is especially interesting. What name is given to the movements of
the leucocytes which enable them to migrate through the walls? What term is applied to
this migration?
The Transformation of an Intermittent Outflow From a Rubber Bulb to a Continuous
Flow from the Extremity of a Tube. (Demonstration.)—A rubber bulb provided with
an inflow and outflow valve is connected with two glass tubes. One of these, on the side
of the inflow valve, dips into a vessel of water; the other, connected to the side of the out¬
flow valve, terminates in a drawn and rather fine extremity. When the bulb is alter¬
nately compressed and released, the water is drawn from the vessel and forced into the
glass tube with the fine extremity. What is the character of the wall of the outflow tube?
What is the character of the outflow of the water? Why?
The outflow tube is removed and replaced by a rubber tube which terminates in a
glass tube having a fine extremity. A short distance from the free end is a stopcock.
With the stopcock open the bulb is compressed and released rhythmically and with mod¬
erate frequency. What is the character of the outflow? Why? The frequency of the ac¬
tion on the bulb is increased. How does that affect the outflow? Why? The stopcock
is partly turned, and the bulb is made to act at various frequencies. Note the effect on
the character of the outflow. The conditions of the experiment as regard frequency of
action of the bulb and degree of resistance offered to the outflow by turning the stop¬
cock, can be so arranged that the outflow will be perfectly steady and continuous.
The intermittent outflow from the bulb will have been transformed into the continuous
outflow from the end of the rubber tube. State the conditions which are necessary for
this transformation. What is the character of the outflow of the blood from the ventri¬
cles? What is the character of the blood flow in arteries, capillaries, and veins? Where
in the vascular system is the variable resistance found that is represented by the stop¬
cock in the apparatus?
The Factors Which Determine Blood Pressure as Exemplified in an Artificial Schema
of the Circulation.—This schema consists of a rubber bulb with inflow and outflow valves
representing the ventricle; of a set of red rubber tubes which diminish in size gradually
from the bulb to a set of glass capillary tubes; these rubber tubes represent the arterial
system; black rubber tubes increasing in size rapidly from the set of capillary tubes to
the inflow side of the bulb represent the venous kystem. The tubes near the bulb are much
larger and thinner on this side than on the arterial side. There is a stopcock near the
end of the arterial system, and there are four mercury manometers—two on the arterial
side, and two on the venous side. The schema is filled with water through a side tube
which is then clamped. With this apparatus the important features of the phenomenon of
pressure as it occurs in the circulatory system will be demonstrated in accordance with
the following outline:
The causes of blood-pressure.
The development of a relatively high minimal pressure in the arteries.
The cause of the maximal pressure.
The significance of the pulse pressure.
The effect of varying the rate and force of action of the bulb.
65
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(a) On the arterial pressure.
(b) On the venous pressure.
The effect of varying the peripheral resistance.
(a) On the arterial pressure.
(b) On the venous pressure.
The Measurement of Arterial Pressure in the Dog. (Demonstration.)—While the
following experiment will be given as a demonstration it can be repeated by groups of
students consisting of six or eight members of the class. The work which each member of
the group is to perform will be apportioned by the Instructor.
All apparatus needed must be mounted and tested before the animal is prepared.
This apparatus is as follows:
(1) A mercury manometer with its float, the writing point of which is kept in eon-
tact with the smoked paper by a silk thread suspended above and kept taut by a small
weight.
(2) The proximal limb of the manometer is connected on the one hand with a bot¬
tle filled with an anti-eoagulating fluid—magnesium sulphate 25 per cent.; sodium citrate
2 per cent.; or sodium carbonate saturated solution—this bottle is provided with a valved
rubber bulb; the proximal limb of the manometer is connected on the other hand, with
a glass tube terminating in a T-tube, one end of which is to be put in communication with
the artery by means of a cannula.
(3) A Jaquet chronograph to register the time in seconds.
(4) A signal magnet.
(5) An inductorium and hand electrodes.
The signal magnet and inductorium are to be placed in circuit with the switch on
the operating table through appropriate binding posts found at the side of the table.
The inductorium must be connected to give tetanizing currents.
(6) If the respiration is to be studied at the same time, a piston recorder or a large
tambour should be placed four or five inches above the writing style of the float. All
writing points must be on the same perpendicular line.
There should be a number of sheets of kymograph paper smoked and ready to slip
over the cylinders of the Hurthle kymograph. The speed of the kymograph is adjusted
to 4 mm. per second. This speed is sufficient to bring out the details of the record.
Release the cylinder from the clockwork and place a smoked paper in position. Bring
the writing style of the float in contact with the smoked paper near the overlap. The
mercury being at the same level in each limb of the manometer, rotate a cylinder by hand
until the paper has made one complete revolution. The line traced by the writing style
is the "base line" or "line of atmospheric pressure." Adjust the writing point of the
signal magnet to write about one centimeter above this line and that of the chronograph
to write the same distance below the line.
Arrange the surgical instruments, cannulae—tracheal and arterial—and a number of
waxed ligatures on the table. Connect the rubber tube to the artificial respiration pipe.
Preparation of the Animal for the Experiment.—About half an hour before the begin¬
ning of the experiment, give a hypodermic injection of morphine sulphate to a dog of med¬
ium size. The dose for the dog is from one to two c.c. of a 2 per cent, solution per kilo-
66
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(a) On the arterial pressure.
(b) On the venous pressure.
The effect of varying the peripheral resistance.
(a) On the arterial pressure.
(b) On the venous pressure.
The Measurement of Arterial Pressure in the Dog. {Demonstration.)— While the
following experiment will be given as a demonstration it can be repeated by groups of
students consisting of six or eight members of the class. The work which each member of
the group is to perform will be apportioned by the Instructor.
All apparatus needed must be mounted and tested before the animal is prepared.
This apparatus is as follows:
(1) A mercury manometer with its float, the writing point of which is kept in con¬
tact with the smoked paper by a silk thread suspended above and kept taut by a small
weight.
(2) The proximal limb of the manometer is connected on the one hand with a bot¬
tle filled with an anti-eoagulating fluid—magnesium sulphate 25 per cent.; sodium citrate
2 per cent.; or sodium carbonate saturated solution—this bottle is provided with a valved
rubber bulb; the proximal limb of the manometer is connected on the other hand, with
a glass tube terminating in a T-tube, one end of which is to be put in communication with
the artery by means of a cannula.
(3) A Jaquet chronograph to register the time in seconds.
(4) A signal magnet.
(5) An induetorium and hand electrodes.
The signal magnet and induetorium are to be placed in circuit with the switch on
the operating table through appropriate binding posts found at the side of the table.
The induetorium must be connected to give tetanizing currents.
(6) If the respiration is to be studied at the same time, a piston recorder or a large
tambour should be placed four or five inches above the writing style of the float. All
writing points must be on the same perpendicular line.
There should be a number of sheets of kymograph paper smoked and ready to slip
over the cylinders of the Hurthle kymograph. The speed of the kymograph is adjusted
to 4 mm. per second. This speed is sufficient to bring out the details of the record.
Release the cylinder from the clockwork and place a smoked paper in position. Bring
the writing style of the float in contact with the smoked paper near the overlap. The
mercury being at the same level in each limb of the manometer, rotate a cylinder by hand
until the paper has made one complete revolution. The line traced by the writing style
is the "base line" or "line of atmospheric pressure." Adjust the writing point of the
signal magnet to write about one centimeter above this line and that of the chronograph
to write the same distance below the line.
Arrange the surgical instruments, cannulae—tracheal and arterial—and a number of
waxed ligatures on the table. Connect the rubber tube to the artificial respiration pipe.
Preparation of the Animal for the Experiment.—About half an hour before the begin¬
ning of the experiment, give a hypodermic injection of morphine sulphate to a dog of med¬
ium size. The dose for the dog is from one to two c.c. of a 2 per cent, solution per kilo-
66
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gram of body weight Weigh the animal to determine the dose. Let one or two members
observe the effects of the drug. In half an hour or less the animal will be stuporous and
can be tied to the holder without difficulty. Handle the animal gently and deliberately. The
dropping bottle having been filled with ether, begin the etherization through a cone made
of gauze. The methods of etherizing, the effects of ether, the means of judging of the
depth of anesthesia should all be learned from appropriate treatises the day before. Watch
the respiration carefully and unremittingly, and if breathing should cease, perform arti¬
ficial respiration, first by rhythmic compres sion of the thorax, and if this does not succeed,
•by means of the respiration apparatus through a tracheal cannula tied securely in the
trachea. Discontinue artificial respiration when normal respiration has returned.
Preparation of the Vagus Nerves and Carotid Artery.—Cut the hair in front of the neck
and throw it in a bucket. Lift the skin with forceps over the supra-sternal notch; make
a small nip with the scissors, insert one bla de through the cut, and split the skin in the
median line as far up as the hyoid bone. Dissect the skin on each side from the underlying
structure, an assistant sponging the blood as the dissection proceeds. Any hemorrhage
beyond ordinary oozing must be arrested, lie careful to avoid the external jugular vein
which is quite superficial and relatively large; it may be exposed for a short distance for
future injections. Cut through the platysma along the ventral border of the sterno-mas-
toid muscle. With a blunt dissector or the handle of a scalpel separate the sterno-mastoid
muscle from the sterno-thyroid and expose the carotid artery, the internal jugular vein, and
the vagus. The vagus nerve can be raiser, from the surrounding structures by means of a
tenaculu; dissect it free for a distance of a few centimeters, using the blunt dissector with
great care. Do this on both sides and pass li atures underneath it and leave them united,
loosely. Do not compress the nerves. Free the carotid artery on the right side from its
sheath for a few centimeters. Pass two ligtures underneath it and leave them united.
Insertion of the Tracheal Cannula.—Separate the sterno-thyroid muscles in the median
line by pulling them apart or with a blunt dissector, being careful to avoid the profuse
hemorrhage that would follow injury to the large veins coursing in front of the
trachea. Pass a piece of linen tape through the eye of a strong aneurism needle; slide
the aneurism needle on the side and push it beneath the trachea to the opposite side. Hold
ing the end of the tape firmly, remove the aneurism needle; the tape must not include any¬
thing more than the trachea. Raise the trachea by means of the tape and, with scissors
cut through the ventral half obliquely from above downward in a place where there are
no large veins. Insert the tracheal cannula through this opening and tie the tape over
it firmly. Connect the cannula by means of a rubber tube about a foot long with an ether
bottle. If any mucus accumulates in the cannula, remove it and clean it out with a piece
of gauze and forceps; replace the cannula in the trachea. The presence of mucus is mani¬
fested by a characteristic bubbling sound.
Preparation of the Crural Nerve and Femoral Vein.—While one member operates on
the neck, another may prepare the crural nerve and the femoral vein. The hair should
be clipped on the inner side of the right thigh. A depression can then be seen or felt be¬
tween the adductor muscles close to the groin. Cut through the skin along this depres¬
sion. With a slight blunt dissection the femoral vessels and the crural nerve will be ex¬
posed. Free the crural nerve for a distance of a few centimeters. Tie a ligature
firmly around it and near the distal end. Cut the nerve distal to the ligature.
67
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The femoral vein may be exposed on the same side or on the left side. The vein must
be carefully dissected free for a short dis .ance. Place a bull-dog forceps on the central
end and a ligature around the distal end. When the vein is distended with blood, tie
the ligature firmly. Put another ligature a -ound the vein. Fill a cannula of appropriate
size, as well as the short piece of rubber tub'ng (about 2 inches long) connected with it,
with saline solution. Clamp the .end of the rubber tube with a stiff bull-dog forceps to
prevent the escape of the solution. Cut through part of the circumference of the vein ob¬
liquely with the ends of the scissors. Insert the cannula and tie it securely with the
ligature. Remove the forceps from the vein. The crural nerve and femoral vein must
be kept covered by the skin until needed.
Insertion of the Arterial Cannula.—A cannula should next be inserted into the right
carotid artery. The arterial cannulae are made of glass and are coated inside with a thin
and smooth film of beeswax to minimize the risk of coagulation. Choose a cannula of
proper size and put it in a beaker filled with the anti-coagulating solution. Tie the up¬
per of the two ligatures placed around the carotid artery. Place a bull-dog forceps on
the artery at its lower end. With the end of the scissors, make a diagonal cut through
about half the circumference of the artery at a point midway between the tied ligature
and the bull-dog forceps. In making this cut, the scissors must be directed toward the car¬
diac end of the artery. This opening into the artery can be made easily by placing a strip
of cardboard across the dorsal aspect of the artery so as to give it a firm support. The
artery may also be grasped by thin forceps from the front and the incision made beneath
the tips of the forceps. Raise the small flap made by the diagonal cut into the artery
and insert into the lumen, the cannula filled with the solution. Hold the cannula in posi¬
tion while an assistant ties the remaining ligature firmly around its neck.
Connection of the Artery With the Manometer.—The proximal limb of the manome¬
ter and the tube running at right angles from it are filled with the anti-coagulating fluid
by compressing the rubber bulb in connection with the supply bottle. Be sure that all
air bubbles have been forced out. Clamp the side branch of the T-tube securely. Adjust
thie animal in such a way that the artery and its contained cannula will be continuous
with the tube in connection with the manometer. This tube is provided with
a short piece of rubber tubing which is to be slipped over the cannula. Compress
the rubber bulb gently and direct the stream of anti-coagulating fluid into the
cannula. As soon as the cannula is filled and while the fluid is still flowing, make the
connection between cannula and manometer; tie very securely. Do not Let the anti-
coagulating fluid come in contact with the vagus nerve. Adjust the height of the mano¬
meter so that the mercury will be on the same level with the heart of the animal.
Press slowly and steadily on the bulb; the fluid being now confined in a closed sys¬
tem its pressure will rise, the mercury on the proximal side will be depressed and will
rise on the distal side. Let the amount of pressure acting on the mercury be about 120
mm.; this will correspond to a rise of the float of 60 mm. from the base line. Before re¬
leasing the rubber bulb, close the stopcock back of the manometer. If the amount of
pressure should have been made too great, it can be decrease 1 by allowing ^he escape of
fluid from the T-tube.
The ...Blood-Pressure Aecord.—Every thing being ready, remove the bull-dog forceps
from the artery and start the kymograph. Observe the movements of the float and the
68
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record traced by its writing style. The small oscillations are due to the action of the
heart; the larger oscillations are due to the respirations.
To bring out the relationship existing between respiration and the larger oscillations
of blood pressure connect a small Fitz pneumograph strapped around the animal's chest,
with the piston recorder or tambour. In what phase of respiration does the blood pressure
rise? In what phase does it fall? Observe carefully, and qualify your statements if neces¬
sary.
The Effect of Changing the Rate and Force of the Heart Beat on the Height of the
Blood Pressure.—While the records of blooa pressure and respiration are going on, raise
the vagus nerves gently by means of the ligatures and sever them in quick succession.
Close and open the key in circuit with the Signal magnet, at each cutting to indicate on
the tracing the precise moment of the experiment. Explain the effects (1) on the blood
pressure, (2) on the respiration.
Adjust the secondary coil of the indue torium for weak currents. Place the periphe¬
ral of the right vagus 011 the electrodes; close the key. Gradually increase the
strength of the secondary currents, stimulating the right vagus at each increase. Repeat
the same procedures on the left vagus. Describe and explain the results. Keep the vagus
nerves covered when not being stimulated
The Effect of Changing the Peripheral Resistance.—(a) Place the crural nerve across
the electrodes and stimulate with a moderately strong current. Note the relatively long
latent period and after effect. What explanation can be offered for these phenomena?
What was the effect (1) on the blood pressure, (2) on the respiration? Explain.
(b) After the blood pressure and respiration have returned to normal, stimulate the
central end of a vagus nerve. Describe and explain the effects on the blood pressure and
respiration.
(c) If a cat or a rabbit is used instead of a dog, the depressor nerve should be iso¬
lated and stimulated. When the vagi are intact the effects of the stimulation are differ¬
ent from those observed with the vagi severed. Wherein does this difference consist ? Give
the reasons.
(d) Prepare some adrenalin chlorid of a strength of 1:10,000 in Ringer's solution and
inject 0.5 cc. into the femoral or external jugular vein. Close the key while the injection
is being made. Describe and explain the results.
(e) Place a pearl of amyl nitrite (5 minims )in a small bottle. Break the pearl and
immediately slip the rubber tube connected with the tracheal cannula into the bottle.
Close the key during the time the amyl nitrite is being inhaled. Remove the bottle in
a few seconds. Where does amyl nitrite act and what is its action? Explain the effect
on blood pressure.
The Effect of Hemorrhage on the Blood Pressure.—As this experiment is to be follow¬
ed immediately by the injection of warm isotonic salt solution, one of the students shou'd
prepare the solution—about 500 cc.—and hold it in readiness at body temperature. In¬
sert a glass cannula into the left femoral artery, using the same method described for the
introduction of a cannula into the right carotid artery. Allow the blood pressure to be
recorded and remove the clamp from the artery. Let the blood flow into a graduate up
to the 20 cc. mark. Has this hemorrhage produced any effect on the Iblood pressure?
If the height of the pressure has changed, how long does it take before it returns to
69
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.
the normal? Remove another 20 cc. of blood, and continue doing so, at intervals, until
the lowering of the pressure has become permanent. How much blood per kilogram of
body weight was it necessary to remove, to produce this effect?
The Effect of the Injection of Isotonic Salt Solution Following a Hemorrhage.—Con¬
nect a funnel with the cannula in the femoral vein. Clamp the vein with forceps. Fill
the rubber tubing and the cannula with the warm saline solution. Take care to exclude
all air bubbles. Immediately after the appearace of the permanent fall of pressure,
pour the warm solution into the funnel, take off the forceps which clamped the vein and
allow the solution to flow in. Observe the tracing of the arterial pressure during the in¬
jection. As soon as the height of the pressure has returned to normal, stop the injection.
How much salt solution was injected?
The Effect of Alloiving Air to Enter a Vein.—Open the external jugular vein and slip
a pipette into it. Force some air into the circulation by compressing the bulb. Note the
effect m* the curve of arterial pressure.
When the animal is dead, open the chest, expose the heart and cut into the right au¬
ricle. Observe the froth in the heart chambers.
THE MEASUREMENT OF B bOOD PRESSURE IN MAN.
Arterial Pressure.—The foregoing experiments have brought out certain fundamental
facts regarding arterial pressure. It has been observed (1) that the pressure is normally at a
considerable height; (2) that it undergoes oscillations. The pressure rises to its maxi¬
mum height with each ventricular systole. This maximum pressure is therefore called the
"systolic pressure." The pressure falls to a minimum point during each ventricular
diastole, hence the minimum pressure is termed the "diastolic pressure." The pressure
therefore oscillates with each heart beat between the diastolic and the systolic level.
Since the increase of pressure represented by the passage from the diastolic to the sys¬
tolic level is responsible for the pulse, this increase of pressure has 'been termed the
"pulse pressure." In any case of measurement of the arterial pressure in man, it is nec¬
essary to estimate both the systolic and the diastolic pressures. The pulse pressure can
be obtained by deducting the diastolic from the systolic pressure.
The methods that are used in the measurement of arterial pressure in man are based
on the principle first enunciated by Marey, that the amount of pressure, applied outside
an artery, which is just sufficient to extinguish the pulsation of the vessel at this point,
is equivalent to the maximum pressure within the artery. The principle underlying the
estimation of the minimum pressure may be stated as follows: if an artery be compressed
(preferably in a concentric manner), the greatest amplitude of the arterial pulsation will
be observed when the amount of the compression is exactly equal to the minimum pres¬
sure within the artery.
The instruments which have been devised for the measurement of arterial pressure
in man are numerous. They may be grouped into three classes: (a) instruments using a
mercury manometer to indicate the amount of compression to which the artery is subject¬
ed; (b) instruments using an ineroid drum; (c) instruments using compressed air with a
water indicator. The aneroid and compressed air instruments are graduated in millimet¬
ers or centimeters of mercury.
These instruments may be classified furthermore, into those employing a cuff, by
means of which circular compression of a segment of a limb may be exerted—upper arm,
70
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finger, wrist—and those employing a pad, either solid or fluid, for the compression of an
individual artery, usually the radial.
Estimation of the Systolic Pressure.—Stanton's and Nicholson's modifications of the
Riva-Rocci apparatus are used. Note that these "sphygmomanometers" are modifica¬
tions of the ordinary U-shaped manometer in that one limb has a considerably larger
cross-section than the other. Any variations of pressure, therefore, occurring in the
wide limb or cistern, will be magnified in the narrow glass tube to which the sliding scale
is attached.
Adjust the rubber cuff surrounded by unyielding material, smoothly around the
upper arm. Connect the rubber tube opening into the cuff with one of the tubes opening
into the cistern. Connect an inflator with the other tube attached to the cistern. See that
the air valve on the inflator is closed. The zero of the scale having been previously placed on a
level with the top of the mercury in the glass tube, everything is now ready.
Feel the pulse in the radial artery. Force air into the system with the inflator. The
air will pass into the cistern and into the rubber cuff around the arm. The pressure ex¬
erted by the air against the arm, and hence against the brachial artery, will be indicated
by the rise of the mercury in the glass tube. Let the pressure rise until the pulse has
fully disappeared from the wrist. Close the stopcock between the inflator and the cis¬
tern. Unscrew the air valve, and allow the pressure to fall very slowly. Watch care¬
fully for the return of the radial pulse. Read the manometer as soon as the first pulsa¬
tion is felt. The reading is that of the systolic pressure.
Estimation of the Diastolic Pressure.—Let the pressure continue to fall. Close the
air valve after each 5 mm. of fall, and observe the oscillations of the mercury column.
The oscillations will gradually increase in amplitude until a certain maximum has been
reached, when they will continue at this maximum for a variable length of time. Watch
the oscillations closely, reading the scale at the lowermost point reached by each oscil¬
lation of the mercury. When the oscillations decrease suddenly the diastolic level of pras-
sure has just been passed. The reading taken at the lowermost point reached by the
high oscillations which immediately precede the sudden fall, is that of the diastolic pres¬
sure.
Korotkow's Auscultatory Method of Measuring the Arterial Pressure.—This meth¬
od being in the majority of eases easier of application, gives very satisfactory and more ac¬
curate results. Connect the apparatus as in the previous experiment. Locate the brachial
artery just below the cuff.
Pump air into the system until the pressure is well above the systolic level. Place a
stethoscope over the brachial artery 'below the cuff, being careful not to exert undue pres¬
sure. Let the pressure in the system fall slowly by allowing a slow escape of the air
through the air valve. When the pressure in the cuff has fallen to such a level that the
blood is able to force its way into the closed artery and separate its flattened walls, a
loud, clear and clicking sound is produced that is heard through the stethoscope. As the
first blood to pass through must be that under highest pressure, the advent of this sound
indicates that the systolic level has been reached. Read immediately the height of the mer¬
cury column in the manometer.
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As the pressure continues to fall the character of the succeeding sounds changes. The
successive sounds have been divided into a number of phases. The first phase is that of
the sound already described as indicating the time at which the systolic pressure is to be
read. The second phase consists of a series of murmurs; the third phase is characterized
by a number of clear, sharp sounds resembling those of the first phase, though less loud.
The fourth phase begins with a sudden passage from the clear, loud tones of the third
phase into a dull sound, which loses rapidly in intensity and disappears. The silence
which follows has been called the fifth phase.
The diastolic level of pressure has been reached when the loud tones of the third
phase give place suddenly to the dull tone of the fourth phase. Read the manometer at
that time. Estimate the pulse pressure.
Name some physiological conditions that affect the blood pressure and describe their
influence briefly.
Venous Pressure.—The blood coursing in the veins is under considerably less pres¬
sure than that flowing through the arteries. Evidently there must be a very large con¬
sumption of the original head of pressure at some point between the end of the small ar¬
teries and the beginning of the veins. Where is this point?
A number of factors, of an accessory character, come into play to maintain the on¬
ward movement of the blood in the veins. Name and explain briefly what these factors
are.
The flow of the venous blood is continuous except in those situations where the veins
are subjected to any pressure acting intermittently. The velocity of the flow is in¬
creased when a contracting muscle presses upon a vein. The same thing occurs with
the changes of intrathoracic pressure which accompany the respiratory movements. For
similar reasons, the venous blood is subjected to more or less localized variations of pres¬
sure. It is of especial interest to note that the pressure changes that occur in the right au¬
ricle make themselves felt for a certain distance backward in the larger veins. These
pressure changes are of sufficient magnitude to give rise to distinct pulsations in these
veins.
Are pulsations ever observed in the smaller veins? If so, under what circumstances?
The Measurement of Venous Pressure in Man.—A simple method can be used for the
measurement of venous pressure when approximate results are sufficient. Observe that
the veins on the back of the hand are more or less dilated. If the hand is raised to a cer¬
tain height this dilatation disappears. Let an arm rest passively on the table; let a fellow-
student raise this arm slowly until the veins on the back of the hand have collapsed.
Measure the vertical distance between the hand and the right auricle. This represents
the height of the venous pressure expressed in centimeters of blood. Change this figure
into millimeters of mercury.
Various instruments have been devised for the measurement of venous pressure. On
account of the low pressure to be measured, the manometer in all these instruments, is a
water manometer. The part of the instrument used to transmit the pressure to the out¬
side of the vein in order to balance its internal pressure, has been varied. In the instru¬
ment to be used, this part consists of a glass cup 20 mm. in diameter, 10 mm. high and
about 1 mm. thick. A side tube connects it by rubber tubing with one of the two
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branches of the proximal end of the manometer. The other branch is connected with a
rubber bulb which can be gradually compressed by means of a pressure screw.
The manometer has been partially filled with water tinted blue, to facilitate the
reading of its level. Adjust the millimeter scale so that its zero will correspond to the level
of the water. Select a prominent vein on the back of the hand on a fairly flat area. Wipe
this area with a little alcohol. Place the glass cup over the vein and hold the cup in place
with a rubber band passed above it and around the hand. With a thin strip of wood,
place a film of flexible collodion at the angle between the glass and skin. Allow plenty
of time for the collodion to dry, then remove the rubber band. The hand must now be
placed at the level of the heart (auricle). As this level changes with the age, sex, posi¬
tion of the body and shape of the chest, an arbitrary level has been selected so that com¬
parative measurements may be made without introducing any serious error. This level
is that of the costal angle. Support the hand at this level, the arm being entirely re¬
laxed. If the hand cannot be conveniently supported at this level, but is placed below
it, the hydrostatic pressure of the column of blood from this point to the heart level
(costal angle) must be deducted from the reading.
The hand being at the heart level, watch the shadow of the vein on the adjacent
skin. Gradually raise the pressure in the system by means of the pressure screw. As soon
as the vein shadow disappears, read the manometer. At this moment, the manometric
pressure upon the vein balances the pressure of the blood within it. The most accurate
results are obtained when the reading is made at the level where slight changes of pres¬
sure cause the vein shadow to come and go promptly just before the vessel collapses en¬
tirely.
Take a deep inspiration; close the glottis and make a steady and prolonged expira¬
tory effort. What effect has this on the venous pressure? Explain.
Change the readings of the water manometer into the equivalents of the mercury
manometer,
THE PULSE.
The Arterial Pulse.—The pulse is a periodic, alternate expansion and recoil of the ar¬
teries. The blood being under a considerable pressure at the end of diastole, causes the
arteries to be distended. Each time that the ventricle contracts and forces its contents
into the aorta, a sudden, additional rise of pressure takes place—the pulse pressure—
which causes a further distension of the arteries. With the cessation of th( ventricular
contraction the arteries recoil, and as the blood passes into the capillaries and veins, the
arterial pressure falls. The recoil is due to the elasticity possessed by the arterial wall.
This elastic recoil, as we have seen, is of importance in the propelling of the blood and in
determining the character of the outflow from the arteries into the capillaries. The sud¬
den rise of pressure which occurs with each discharge of the ventricular contents, travels
from the root of the aorta to the ends of the arterial system in the form of a wave. We
may expect, therefore, that various points of the arterial system will expand and recoil at
different times depending on their distance from the root of the aorta. The expansion
and recoil—or pulse—at any one point of an artery is simply an indication of the passage
of the wave of pressure at that point.
The pulse can be studied by feeling the artery and determining, through the sensations
73
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branches of the
rubber bulb
The manome
reading of its lev
of the water,
this area with a
with a rubber b
place a film of
of time for the
placed at the le
tion of the bod
parative measur
is that of the costal angle. Support
laxed. If the hand cannot be conveniently supported at this level,
it, the hydrostatic pressure of the column of blood from this point to the heart level
(costal angle) must be deducted from the reading.
The hand being at the heart level, watch the shadow of the vein on the adjacent
skin. Gradually raise the pressure in the system by means of the pressure screw. As soon
as the vein shadow disappears, read the manometer. At this moment, the manometric
pressure upon the vein balances the pressure of the blood within it. The most accurate
results are obtained when the reading is made at the level where slight changes of pres¬
sure cause the vein shadow to come and go promptly just before the vessel collapses en¬
tirely.
Take a deep inspiration; close the glottis and make a steady and prolonged expira¬
tory effort. What effect has this on the venous pressure? Explain.
Change the readings of the water manometer into the equivalents of the mercury
manometer.
THE PULSE.
The Arterial Pulse.—The pulse is a periodic, alternate expansion and recoil of the ar¬
teries. The blood being under a considerable pressure at the end of diastole, causes the
arteries to be distended. Each time that the ventricle contracts and forces its contents
into the aorta, a sudden, additional rise of pressure takes place—the pulse pressure:—
which causes a further distension of the arteries. With the cessation of the ventricular
contraction the arteries recoil, and as the blood passes into the capillaries and veins, the
arterial pressure falls. The recoil is due to the elasticity possessed by the arterial wall.
This elastic recoil, as we have seen, is of importance in the propelling of the blood and in
determining the character of the outflow from the arteries into the capillaries. The sud¬
den rise of pressure which occurs with each discharge of the ventricular contents, travels
from the root of the aorta to the ends of the arterial system in the form of a wave. We
may expect, therefore, that various points of the arterial system will expand and recoil at
different times depending on their distance from the root of the aorta. The expansion
and recoil—or pulse—at any one point of an artery is simply an indication of the passage
of the wave of pressure at that point.
The pulse can be studied by feeling the artery and determining, through the sensations
73
2ted from the reading.
heart level, watch the shadow of the vein on the adjacent
essure in the system by means of the pressure screw. As soon
rs, read the manometer. At this moment, the manometric
aces the pressure of the blood within it. The most accurate
e reading is made at the level where slight changes of pres¬
to come and go promptly just before the vessel collapses en-
; close the glottis and make a steady and prolonged expira-
this on the venous pressure? Explain,
the water manometer into the equivalents of the mercury
THE PULSE.
pulse is a periodic, alternate expansion and recoil of the ar-
:r a considerable pressure at the end of diastole, causes the
ih time that the ventricle contracts and forces its contents
tional rise of pressure takes place—the pulse pressure;—
ision of the arteries. With the cessation of th< ventricular
, and as the blood passes into the capillaries and veins, the
recoil is due to the elasticity possessed by the arterial wall.
! seen, is of importance in the propelling of the blood and in
the outflow from the arteries into the capillaries. The sud-
curs with each discharge of the ventricular contents, travels
the ends of the arterial system in the form of a wave. We
irious points of the arterial system will expand and recoil at
: their distance from the root of the aorta. The expansion
one point of an artery is simply an indication of the passage
lat point.
by feeling the artery and determining, through the sensations
73
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produced by the successive expansions and recoils, whether its characteristics are normal
or abnormal. The pulse may also be studied by recording the movements of the arterial
wall. When the variations of pressure taking place within the artery are recorded, the
record is a "pressure-pulse" record. When the changes of volume of the artery are re¬
corded, the record is a "volume-pulse" record. The first type of record can be obtained
with an apparatus called a "sphygmograph;" the pulse curve is called a "sphymo-
gram." The second type of pulse record can be obtained by means of a "plethysmo-
graph."
Study of the Pulse with the Artificial Schema, (a) By the Sense of Touch.—Adjust
the peripheral resistance in the schema and compress the bulb at such a rate that there
will be established a moderately high minimum pressure. Feel the rubber tube on the
arterial side. Observe that it is necessary to press upon it with a certain degree of force
in order to obtain the full evidence of the pulsations.
Are the pulsations rhythmical? What is their frequency? Do the pulsations come
up quickly, or slowly under the finger? Are the pulsations large or small? Do the con¬
tents of the tube feel tense or soft?
Vary the conditions of the experiment: (1) as to the character of the action on the
bulb; (2) as to the degree of peripheral resistance. Describe the effects of these varia¬
tions on the different characteristics of the pulsations.
Study these characteristics on the radial artery of a number of fellow students. Use
correct clinical terms in recording your observations.
(b) By the Graphic Method.—Place a receiving tambour of suitable form on the ar¬
terial tube of the schema. Connect this tambour with a recording tambour whose lever
is in contact with a slightly smoked cylinder. The tubing connecting the tambours is pro¬
vided with a side tube to enable the necessary adjustments to be made without causing
any movement of the recording lever. Record the pulsations of the tube, the cylinder re¬
volving moderately fast. Study the characteristics of the record. How do the lines of
ascent and descent differ from each other? What is the "dicrotic" wave? Give a theory
of its formation.
Take records of pulsations near the bulb and near the end of the arterial tube. What
differences are there in the records? Give the reasons for these differences. Vary the
conditions of the experiment as explained in the foregoing experiment. Note the results;
bring out the relationship existing between the observed change in the record and the
modification in the experiment which is responsible for it,
The Velocity of the Pulse Wave.—Place two receiving tambours on the arterial tube
of the schema, one near the bulb and the other one meter farther away. Connect these
tambours with two recording tambours arranged to write one below the other and on
the same perpendicular line. The tubing connecting the tambours must be of exactly the
same length. Arrange a time marker to record 50 vibrations per second on a line with
the levers. Compress the bulb rhythmically until a moderately high minimum pressure
has been established. Clamp the side tubes on the tambour tubing. Start the time-mark¬
er and then the kymograph, full speed. After one revolution, stop the kymograph and
study the curves.
74
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Draw ordinates with the levers at the following points: (1) the foot of the line of as¬
cent of the upper curve; (2) the simultaneous point on the lower curve; (3) the foot of
the line of ascent of the lower curve. Note that the lever recording the movement of
the tube nearest the bulb rose before the other lever in connection with the tube farther
away. The difference in time, in the rise of the levers, represents the time that it took
the pulse wave to pass from one receiving tambour to the other. With the T-rule draw
ordinates from the points on the lower curve marked by the ordinates on that curve, to
the chronographic tracing.
How much time did it take for the pulse wave to travel from one receiving tambour
to the other? Calculate the velocity of the pulse wave per second. Change the periphe¬
ral resistance in different directions and determine what effect the changes have on the
velocity of the pulse wave.
Feel the carotid pulse and the radial p ulse simultaneously in a fellow student. Which
pulsation is felt first? Why?
The Recording of the Carotid Pulse.—Smoke a cylinder lightly. Mount a recording
tambour provided with a light straw lever, on the adjustable stand. Mount a time mark¬
er to write a short distance below the lever, and connect it with the vibrating interrup¬
ter so as to obtain 10 vibrations per second. Connect a small funnel with the end of the
tubing. Bring the writing point of the lever lightly against the smoked paper. Start the
time-marker. Let a fellow student apply 1 he funnel over that part of the neck where the
best pulsation of the carotid artery is felt. This point is usually in front of the sterno-
mastoid muscle at the level of the upper border of the thyroid cartilage. Close the side
tube; start the cylinder revolving moderately fast. After one revolution stop the cylin¬
der.
Study the pulse curve or sphygmogram just obtained. Note the characteristics of
the line of ascent and of the line of descent. How many secondary waves are there on the
line of descent? Draw an ordinate through the dicrotic notch. Estimate the duration (1)
of the cardiac cycle, (2) of systole, and (3) of diastole. What are the conditions which
favor a high dicrotic wave?
The Venous Pulse.—It has been stated that the variations of intra-auricular pres¬
sure are propagated for a certain distance into the large veins near the heart. The pulsa¬
tions in the veins which are thus occasioned can be seen in a large number of individuals
at the root of the neck over the position of the right internal jugular vein. Less frequent¬
ly, they may be seen over the left internal jugular or over the external jugular veins.
A record of these pulsations, taken simultaneously with the carotid pulse and the
cardiac beat, is of great value in the study of the heart's action in health and in disease.
In fact, our modern conceptions of heart disease have been gained largely through the
aid of the venous pulse.
Mount three tambours on the adjustable stand and adjust the levers to write on the
same perpendicular line. Arrange a time-marker to give 10 vibrations per second, and
to write a short distance below the levers. Smoke a cylinder lightly. Adjust the writ¬
ing points against the smoked paper with light pressure. Let a student with bared
chest lie on the table. Locate the apex beat; strap the Jaquet cardiograph around the
chest and place the button of the tambour exactly over the apex beat. Connect the lower-
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Draw ordinates with the levers at the following points: (1) the foot of the line of as¬
cent of the upper curve; (2) the simultaneous point on the lower curve; (3) the foot of
the line of ascent of the lower curve. Note that the lever recording the movement of
the tube nearest the bulb rose before the other lever in connection with the tube farther
away. The difference in time, in the rise of the levers, represents the time that it took
the pulse wave to pass from one receiving tambour to the other. With the T-rule draw
ordinates from the points on the lower curve marked by the ordinates on that curve, to
the chronographic tracing.
How much time did it take for the pulse wave to travel from one receiving tambour
to the other? Calculate the velocity of the pulse wave per second. Change the periphe¬
ral resistance in different directions and determine what effect the changes have on the
velocity of the pulse wave.
Feel the carotid pulse and the radial p ulse simultaneously in a fellow student. Which
pulsation is felt first? Why?
The Recording of the Carotid Pulse.—Smoke a cylinder lightly. Mount a recording
tambour provided with a light straw lever, on the adjustable stand. Mount a time mark¬
er to write a short distance below the lever, and connect it with the vibrating interrup¬
ter so as to obtain 10 vibrations per second. Connect a small funnel with the end of the
tubing. Bring the writing point of the lever lightly against the smoked paper. Start the
time-marker. Let a fellow student apply 1 he funnel over that part of the neck where the
best pulsation of the carotid artery is felt. This point is usually in front of the sterno-
mastoid muscle at the level of the upper border of the thyroid cartilage. Close the side
tube; start the cylinder revolving moderately fast. After one revolution stop the cylin¬
der.
Study the pulse curve or sphygmogram just obtained. Note ,the characteristics of
the line of ascent and of the line of descent. How many secondary waves are there on the
line of descent? Draw an ordinate through the dicrotic notch. Estimate the duration (1)
of the cardiac cycle, (2) of systole, and (3) of diastole. What are the conditions which
favor a high dicrotic wave?
The Venous Pulse.—It has been stated that the variations of intra-auricular pres¬
sure are propagated for a certain distance into the large veins near the heart. The pulsa¬
tions in the veins which are thus occasioned can be seen in a large number of individuals
at the root of the neck over the position of the right internal jugular vein. Less frequent¬
ly, they may be seen over the left internal jugular or over the external jugular veins.
A record of these pulsations, taken simultaneously with the carotid pulse and the
cardiac beat, is of great value in the study of the heart's action in health and in disease.
In fact, our modern conceptions of heart disease have been gained largely through the
aid of the venous pulse.
Mount three tambours on the adjustable stand and adjust the levers to write on the
same perpendicular line. Arrange a time-marker to give 10 vibrations per second, and
to write a short distance below the levers. Smoke a cylinder lightly. Adjust the writ¬
ing points against the smoked paper with light pressure. Let a student with bared
chest lie on the table. Locate the apex beat; strap the Jaquet cardiograph around the
chest and place the button of the tambour exactly over the apex beat. Connect the lower-
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most recording tambour with the cardiograph. Test the pulsations by closing the slde
tube and if necessary, readjust the cardiograph or the amount of pressure of the button-
Connect a small funnel with the tubing of the middle tambour. Find the p'*"* in
the neck where the best carotid pulsations can be obtained.
The pulsations of the vein are collected with a low metallic capsule having a 'flat side
and called a "Mackenzie receiver." The pulsations are best located with the eye. Let
the subject incline the head slightly toward the right shoulder and turn the cv'in toward
e left in order to relax the stemo-mastoid. Connect the receiver with the tub'ng the
upper tambour. Place the receiver over the pulsating tissues, flat side against the clavi¬
cle and see that its edges are everywhere in contact with the skin. Test the pulsations
by closing the side tube.
When everything is in readiness, start the time-marker and record the pulsations of
the jugular vein, carotid artery, and the heart's apex simultaneously, .on a moderately
fast cylinder.
^■ote that the venous pulse as seen in any one cardiac cycle consists of three positive
waves and of three negative waves. To bring out the relationship of these waves with
t e various phases of the cardiac cycle, draw ordinates through the foot point of each of
the positive waves, and simultaneous ordinates through the sphygmogram and the cardio¬
gram. These ordinates must be drawn with the recording levers before the stand has
been moved. Notice that one of these ordinates falls well in front of the upstroke of the
cardiogram. This indicates the beginning of the auricular contraction. Label this posi¬
tive wave: a. In what phase of the cardiac cycle does the second positive wave fall?
Label this wave: j. (this is the c wave of Mackenzie). Does it begin before, or at the same
time as the carotid expansion? How is it produced? In what part of the cardiac cycle
does the third positive wave fall? Label this wave: z\ Give an explanation of its produc¬
tion. Remember that the as interval represents approximately, the time of propagation
of the impulse from auricle to ventricles. It is called the "conduction time." Measure
the a-s interval.
Explain the production of the first negative wave. Label the second and third neirt-
tives waves Af (auricular filling) and Vf (ventricular filling), respectively. (These are des¬
ignated x and y by Mackenzie.) Explain their production.
The relationship existing between the features of the venous pulse and those of the
sphygmogram and cardiogram can be made out more accurately by using a hieher
of the kymograph and a time marker vibrating 50 or 100 times a second.
76
Lde
on. iftp. J^ajal Hstabo, Hem pf Kan.
m
side
Let
vai\l
1 vhe
lavi-
tions
The term "metabolism" is applied to the totality of the
chemical changes taking place in the tissues. The extent of these
changes may be determined by comparing the amount of the various food
constituents introduced in the body with the amount of the excretory
products discharged from the body. Name (l) the constituents cf food;
;S) the waste products of tissue metabolism. What is meant by (a) an-
abolism; (b) oatabolism?
s of The process underlying the chemical changes, whereby the
iteVy food constituents are disintegrated into waste materials, is essent¬
ially one cf oxidation. During this disintegration the potential en¬
ergy stored in the food molecules is set free as kinetic energy and
o&\\.we
vrih appears as heat, movement and electricity. It is, therefore, possible
eachoi :t. determine the extent of the chemical changes taking place in the
^cardio- *^99ue9 by comparing the energy intake with the energy output. The
, . icst convenient unit of energy, in this connection, is the "calorie".
Hat is a 'l) large calorie; ;2) small calorie? What is the differ¬
ence between the physical and physiological energy or heat value of
;he various food principles? Explain in full.
ka oi the
this post-
wave ia\\:
The energy value of a diet may be calculated by multiply-
'ardiac cycle jig the quantity of'each food principle by its calorific value, ( in-
»f -sproduc- Lirect oalorimetxy ). Calculate the energy value of a standard diet.
t." Measure The energy value of a diet may likewise be estimated while
be food is undergoing oxidation in the body, by measuring the heat
d third new--^berated from the body, { direct calorimetry ). In such a case the
' ^amount of heat liberated is lees than the amount that should theoretic-
8 .11y be obtained. How is this to be. accounted for? How can the total
•nergy value of the diet be arrived at, in direct calorimetry?
those of tk'isouss all possibilities that might account for a discrepancy between
higher speed icasured value and theoretical value.
A.s observations have to be made on different individuals,
.t is essential, for comparative purposes, that the. conditions under
rhioh the observations ar® made be uniform. All conditions affecting
be rate of metabolism must be carefully controlled, for it is an es~
iablished fact that the rate at which heat- is liberated in the body
index goes wide flu#tuat lore, even in the same individual, under differ¬
ent conditions. The most important of the conditions influencing the
'ate of metabolism, are: 'l) muscular exercise, (3) the ingestion cf
food. What is the influence of (a) muscular exercise; muscle tonus;
b) food, on the rate of metabolism? What is meant by the "specific
iynamic action" of the foodstuffs? For which foodstuff is it highest?
"ive all answers in quantitative terms.
In estimating the fundamental rate of metabolism for pur—
joses of comparison, it is necessary to eliminate the influence of
/pod and muscular action. This is accomplished by determining the en¬
ergy metabolism from fifteen to eighteen hours after the last meal,
tbe individual lying down, completely at rest. The metabolism deter¬
mined under these conditions is called the "basal metabolism". It is
tbe lowest possible metabolism for the waking state.
1
("■)
A comparison of the basal metabolism in individuals of differ©]
sizes has shown that body weight cannot be taken as a criterion., ^ Mori
uniform results hc.ve been obtained by using the body surface as the
criterion for comparison. Why should this be the case? As the rate
of metabolism must of necessity be determined by the mass of living
tissues md its activity, differences are to be ooserved in ^individ¬
uals having the same body surface but of different states of nutritic:
different age, or sex. Consult a ohc.rt showing the basAl metabolism,
estimated per square meter of body surface per hour, for different ag«
The basal metabolism is altered in certain pathological
conditions. For this reason, the determination of the basal metabol¬
ism has become a valuable aid in diagnosis and in following the effeci
of treatment.
numerous determinations, made under various conditions,
have demonstrated that the intake of oxygen and output of carbon diox¬
ide are proportional to the energy liberated in the body. Hence it if
that a determination of the respiratory exchange rrn.y serve as a means
of calculating the energy exchange ( indirect calorimetry ). It has
furthermore been shown that the amount of oxygen consumed is a better
index of the total metabolism than the amount of carbon dioxide exhale
"
The most convenient apparatus for clinical work is the on#
devised by Benedict, with this apparatus, neither gas analyses nor
weighings are necessary only in case the carbon dioxide output is to \\
estimated, in order to compute the respiratory quotient, Whet is meaz
by "respiratory quotient"? What is its significance?
•
£he Benedijlt^MetabolJ^srg Apparatus,. The apparatus consiste
essentially of a "spirometer containing oxygen. The spirometer is con¬
nected to a blower driven by an electric motor. From the blower there
Issues a narrow tube which connects with three jars, two of which con¬
tain calcium chloride, the remaining jar containing soda lime. These
three jars are used when both oxygen intake and carbon dioxide output
are to be estimated. In case- the consumption of oxygen alone is to be
measured, the only jar necessary is the one containing soda lime. Why
The tu>e issuing from the jars goes to a valve-c-that may be terned so
to connect- the tubing with a mouth piece. From the valve another,-
jidor tube returns to "the spirometer. The subject inhales from the
mixture of air and oxygen contained in this closed system and kept in
circulation by the blo-er, and exhales into it <_.s in natural respir¬
ation.
The, pet_ermin&fjion ilf.t^e^Basal_Metabplism. The joints
have all been tested for~~meaks and the rate ofxventilation has been
adjusted to that required for comfortable breathing. The student who
is to serve <.s subject must have been without food not less than fif¬
teen hours, Let him lie down comfortably while the members of the
grdup study the apparatus. The operator then places the nose clip on
'cue subject's nose so that the rubber grips cover the nostrils and the
, Tire part extends outward from the upper lip; he then tightener, the-
I shrew until no, air can be blown through the nose. Ths^-rubber mouth
flece is next inserted between the lips and teeth and the subject
breathes for a minute or two to the open air. IXurAag this time^-^ocunt
r"0
the pulse aji^'-th.e^"ire3prlx64rioiis''"for a full minute, . The metal tube cc
nection is then .inserted into the mouth piece and the whole connected
to the apparatus. Allow the. subject to breathe for a few minutes wil..
the valve open to the air, until"quiet, normal breathing action has I
been- established.
As soon as breathing is normal, turn the valve so that tj
subject begins breathing in and out of the system* Start the motor.J
Hots the height to which the spirometer rises at the end of a seriesj
regular, normal expirations. Head the spirometer scale at the end o
normal expiration. Record the reading, the time and the temperature
the spirometer.
Allow the test to continue for exactly fifteen minutes,
the meanwhile, and without disturbing the subject, the pulse and res
irations are counted and noted at the beginning, in the middle and b
ward the end of the test.
As soon as the time has expired, read the spirometer sea'
at the end of an expiration and the temperature in the spirometer.
The difference between the reading of the spirometer sea
at the beginning of the test and that at the end of the test, shows
volume of oxygen that has been consumed by the subject.
The volume of a gas varies directly as the temperature, <
inversely as the barometric pressure. Hence it is necessary for pur,
ses of comparison to reduce all readings to a given standard. This
standard is a temperature of 0° Centigrade and a barometric pressure
730 mm. Hg. Moreover, since the expired air is saturated with water
the pressure due to water vapor mast be subtracted from barometric pi
sure acting on the gas. As the volume of the mercury in the baronet*
varies likewise with the temperature, the reading must be corrected i
a temperature of 0° 0. Consult a table showing the correction neces*
ary for various temperatures and barometric heights.
The following formula is used in reducing the observed vt
ume of gas to standard temperature and pressure:
vo» __Ii
760 x {1 .y 0.003335 t)
in which Yo represents the corrected volume, V the volume observed, E
the barometric pressure corrected for temperature, T the pressure of
the water vapor ( aqueous tension ) at the temperature of the reading'
and t the average temperature in the spirometer in degrees centigrade'
O'iOO 3635 is the coefficient of expansion of gases.
Calculation qf_the_C alqr _i c. Y a lu e ^ Consult a table show in
the heat value of i liter o~f oxygen at various respiratory quotients.
From this table calculate the heat value of the volume of oxygen con¬
sumed per hour, supposing the respiratory quotient be 0.88, Estimate
the caloric value (1) per kilogram of body weight per hour; (8) per
square meter of body surface per hour. The area of the body surface
may be obtained by referring to the chart showing the surface area of
She body for various weights and heights*
Compare your results with the chart showing the basal me¬
tabolism per square meter per hour for various'ages.
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1.
Astigmatj-sm.— Draw two lines on a card,one horizontal,
"the other vertical. Hold the card perpindicular to the line
of vision and determine the far and near points for (1) the
vertical line, (3) the horixont&l line. It is preferable to
Use but one eye in making this test. With most people the
vertical line appears distinct at a greater distance than the
horzontal line. Furthermore, a fine horizontal line can be
brought closer to the eye than a vertical line without be¬
coming indistinct .From these observations it follows that t
the refracting power of the eye in the horizontal and verti¬
cal direction is not equal; the refracting pgwer is greater in
in the vertical meridian than in the horizontal. The resulting
nag optical defect is called "astigmatism" or better, "astigsia
fc&". Why?
Astigmatism may be due to an equality inequality of
curvature of the different meridians of the cornea or lens.It
is, however,more often found in the cornea than in the lens
although it may be present in both in the same eye. The nor¬
mal cornea is seldom truly spherical in shape but rather el-
lip soidal,the focus of the vertical meridian being slightly
shorter than that of the horizontal. When this condition ob¬
tains in anexaggerated form it constitutes "regular astigma¬
tism" "with the rule". When the horizontal meridian has the
shorter focus the astigmatism is said to be "against therule".
Draw the paths of parallel rays of light passing into an
eye having astigmatism with the rule,(l) in simple hyperopic
astigmatism; (3; in simple myotic astigmatism.
The Measurement of Corneal. Asti^mtism. — The instrument
used for this purpose i3 oallacF-an -tk^htJmJjmometer" but as it
measures only the curvature of the cornea in its different
meridians, it should be called a "keratometer".
The instrument consists of a telescope containing a Wol-
laston birefrangent prism of Iceland spar placed between two
biconvex lenses. Mounted on the telescope is a graduated aro
eatable of being ratated t hrough a complete circle, the de¬
cree of rotation being shown on a dial in front of the eye-
fiece The arc supports two ground glass objects,illuminated
from behind and called "mires" or "targets". One of the mixes
. unilateral in shape, the other o f the same size has
1 %ide cut into six steps; both mires are divided in the
°vidle by a black line. The instrument is mounted on a tripod
that can be moved back and forth for the purpose of focusing.
He natient's forehead and chin are supported by a frame and
Uiustable chin rest.
a J The members of the class will act alternately as subject
a ob8Crver*Iie't 0^ with his face supported in
h frame, the eye to be studied on a level with the barrel
/ the telescope. The arc supporting the mires occupies the
rizontal position. The observer looking through the eye-
k- re focuses the center of the subject1 s cornea until two
?ffoee of each mire appear sharp and distinct. The obsexva-
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tions axe to be confinadto the central images only, the pe¬
ripheral imageb b^ing ignored. Slide the mixes on the arc,if
necessary, u nt il the central images occupy the center or pole
of the cornea in such a way that their inner e dges just touch
and that the black line in each forms one continuous line. In
order to^ accomplish this, itn*^S fi^cessary to rotate the arc
from right to left or from left to right, but not beyond 45
degrees either way. This position when obtained is called the
"primary position" and indicates the meridian of .least re-
fraution . Read the axis or meridian on the dial.
Now, turn the arc until it occupies a position at right
angles to this meridian —the "secondary position" — and ob¬
serve the images of the mires upon the oornea. If they are
st ill in appoeitio n,the curvature of the cornea is uniform
throughout; there is no corneal astigmafc ism. If, however, the
images overlap, the curvature of the cornea is greater in this
meridian than in the first one. As each step on the divided
mire represents 1 D.j the degree of astigmatism can be estim¬
ated by ths amou nt of overlapping.
It sometimes happens that in pa&eing fr om the primary to
the secondary position,the images of the mires separate. In
such a case, what is the secondary position should have-been
the primary and the necessary change must be made.
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ECTXLIBEIUM
mm mm mm mm mm
Vestibular Tesfs#
2«t The nystagmus, past^poi&ting and falling, after turning,
2? ^ The turning-Chair must have a head-rest which will
nolo, the head 30 forward, a foot-rest' and a atop-pedal,
(a) KY3TAGHCJ3. Head 30 forward; turn candidate to the
right, eyes closed, 1© times in exactly 20 seconds, THE instant
the chair is stopped click the stop—watch; candidate opens his
eyes and looks straight ahead ot some distant point. There
shluia occur a horizontal nystagmus to the left of 26 seconds
duration# Candidate then closes his eyes and is turned to the
left; there should occur a horizontal nystagmus to the right of
26 seconds duration# The variation of 6 seconds is allowable#
(b) DOIHTIHG# (l) Candidate closes eyes sitting in cbair
facing examiner, touches the examiner's finger held in front of
him, raises his arm to perpehdicular position, lowers the arm,
and attempts to find the examiner's finger# first the right ana;
then the left arm# The normal is always able to find the finger.
(2) The pointing test is again r4peated after turning to the*
right, 10 turns ih 10 seconds# During the last turn the stop-
pedal is released, and as the chair comes into position it be¬
comes'locked^ The right ana is tested, then the left, then the
right, then to the left, until he ceases to past-point# The
normal will past-point to the right 3 times with each arm# (3)
bpeat pointing test, after turning to the left#
Tc) FiXDIUG. Candidates head is inclined 90° forward#
bain to the ri&ht, 5 turns in 10 seconds# On stopping, candidate
raises his head and should fall to the right. This tests the Q
vertical semicircular canals# Turn to the left, head forward 9C
On stopping, the candidate raises his'head and should fall tc
the left. Unless each test is normal, it is a cause for rejection#
Special Regulations Ho# 50 Aviation Section, Signal Corps,
far Department and Circular Ho. 2, War Department Hovember 1, lsafc
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