COLUMBIA UNIVERSITY EDWARD G. JANEWAY MEMORIAL LIBRARY 4* Si 7 # J/L^^^y •. % \" ' " h ■ . » • \ .\ )\ \\ ) Digitized by the Internet Archive in 2011 with funding from Open Knowledge Commons http://www.archive.org/details/imaginationidealOOhert IMAGINATION AND IDEALISM IN THE MEDICAL SCIENCES CHRISTIAN A. HERTER, M.D. Professor of Pharmacology, Columbia University NEW YORK CITY An Address Delivered to the College of Physicians and Surgeons, Columbia University, Sept. 23, 1909, at the Opening of the Medical School PBM8 "i jiii. Ambbicah (Medical Association .".::.", I)i;ahiiuu.n Avio i;k Chicago IMAGINATION AND IDEALISM IN THE MEDICAL SCIENCES* CHRISTIAN A. HERTER, M.D. Professor of Pharmacology, Columbia University NEW YORK The presidential invitation in response to which I am about to address yon to-day was welcome to me because it offered a rare chance to express some views of medical progress which I think are too seldom presented to the student. I have in mind the influence of imagination and idealism on the growth of medical discovery. Viv- idly recalling, as I do, the experiences of my own stu- dent days, more than a quarter century past, I fancy you as coming to the acquisition of the myriad facts of medicine with little to tell you of the intellectual forces and historical sequences by which those facts have emerged. If this surmise be correct, it follows that you incline to take a static rather than a dynamic view of the nature of scientific medicine, in the sense that you regard medical lore as something much more fixed than is actually the case. In reality, our science is fortunately plastic, constantly subject to revision of its facts, and r ready to welcome new interpretations of old facts :i- well as new discoveries, both great and small. This * An ndrlioHH delivered at the College of Physicians and Sur- ilumbla University, Sept. 2'.',, 1!)09, at the opening of the Medical BCQOOl. 3 very plasticity it is that makes progress attainable and fascinates our minds. But our text-books and our lec- tures are necessarily conservative and dispose us strongly to the notion of fixity of facts, making our minds statical in conception. I would like to dispel, in a measure, this retarding conception by telling you some- thing of the ways in which gifted and trained minds have enriched the medical sciences by significant dis- coveries. And of the qualities underlying such dis- coveries I would emphasize especially the role of imagi- nation and idealism. The fine humanitarian aim of medicine always has been and always will be one of the features that make men love to practice the art. And the idealism that delights in the relief of human suffering and disability will remain alive so long as the healing art itself. But we must not blind ourselves to the fact that this very attitude of eager desire to help our fellows in distress is a source of weakness as well as a pillar of strength. For he who would answer the calls of the sick must resort to direct methods and must generally tread the paths of the obvious. He has not time to turn aside to the indi- rect ways of winning the citadel, nor, indeed, is he likely to be in that frame of mind which urges to such an approach; he is preoccupied with the crying needs of the suffering or dying man committed to his charge. Yet it is growing every day clearer that the progress of the medical sciences depends in a remarkable degree on discoveries made by indirect methods — that is, by meth- ods not looking to the immediate relief of disease. These discoveries are made chiefly by men who, while in deep sympathy with the humanitarian aims of medi- cine, nevertheless find time to turn aside to studies and experiments from which the active practitioners are, in general, excluded, by the circumstances of their lives and the intensely practical nature of their vocation. There was a time when the alert physician or surgeon, with little or no training in the experimental method, might make important contributions to knowledge by following rather evident suggestions derived from the study of patients. The Romans, operating for stone in the blad- der; Pare, using the ligature to check hemorrhage on the field of battle; McDowell, successfully removing ovarian tumors, give us examples of great advances along rather obvious lines of development. To-day the chances for significant progress in such evident directions, although not exhausted, are far less frequent. The golden nuggets at or near the surface of things have been for the greater part discovered, it seems safe to say. We must dig deeper to find new ones of equal value, and we must often dig circuitously, with mere hints for guides. Our most effective tools are to be found in the experimental laboratory, where the fundamental sciences, physics and chemistry, come to the aid of physiology, biology, pathology and psj-chology. I should like to tell you of some of the many instances in which these sciences have come to the succor of medicine and have brought her riches of knowledge unattainable had she been limited to resources belonging to the accumulated experience which makes up the accepted material of medical teaching. If I incidentally say something of the personality of the men who have been the living instru- ments of this progress, it is in order to give you occa- sional glimpses into the workings of some of the most original and productive of minds. I like to think of medicine in our day as an ever- broadening and deepening river, fed by the limpid -tream.- of pure science. The river at its borders has its eddies and currents, expressive of certain doubts and errors that fringe all progress; but it makes continuous advances on the way to the ocean of its destiny. Very gradual has been the progress of its widening and deep- ening, for it is a product of human ingenuity and arti- fice, and only skilled engineers could direct the isolated currents of science into the somewhat sluggish stream of medical utility. The names of some of the greatest of these engineers are familiar to you — Vesalius, Harvey, Malpighi, John Hunter, Claude Bernard, Helmholtz, Virchow, Metchnikoff, Pasteur, Lister, Koch, Behring, Ehrlich, Emil Fischer, Weigert, Wright, Theobald Smith, Flexner. Different as have been the achieve- ments of these men, there are some qualities of mind and of heart which nearly all of them have shown in ample measure, and of such qualities none are more evident than imagination, or play of fancy, and personal idealism, using the latter term to mean a readiness to make sacrifices for the sake of lofty achievement. And I think we are quite safe in making the generalization that the discoveries for which we hold these thinkers in honor would have been impossible but for the exercise of these qualities. If this be true, the fact furnishes us with a clue to present tendencies in medicine and shows us to what sorts of gifts we have to look for the signifi- cant advances of the future. I, therefore, hope to make good my generalizations by a series of examples. If we look over any list of the names of the makers of modern medicine, we shall find that they may be classed in two main and definite groups, according to the intellectual trend for which they stand. One group holds the men who look at the problems of medical science largely from the standpoint of structure and arrangement. They have the instincts and interests of the morphologists. They represent anatomy, embryol- ogy, pathological anatomy and histology. They have usually been men of powerful and logical minds, craving the positive, the definite and the attainable, either shun- ning somewhat the speculative aspects of science, or moving uncomfortably in the midst of ill-defined or challengeable facts. In this list belong Vesalius, von Baer, Bichat, Virchow and Weigert, who represent with maximal distinction the group of investigators with dominant morphological tendencies. In sharp contrast with this definite type stands the second group, made up of men whose interests lie in the study of function, rather than structure, and whose minds, far from being dismayed by the speculative aspects of their studies, invite such speculation so long as it is severely controlled by frequent appeals to facts won by experiment. The members of this small group are dynamically minded, highly imaginative, delighting in the play of forces. They are essentially experimental- ists, and their thoughts in leisure hours, as in the hours of work, turn always restlessly and uncontrollably in the same direction — to the planning of new experiments designed to answer the questions uppermost in con- sciousness, questions having nearly always to do with the phenomena of living beings. Claude Bernard, Helm- holtz, Pasteur and Ehrlich are the unexcelled prototypes of investigators of life-phenomena in medicine, and we shall not go far astray if we fancy them as spirits inspired by "All that is great and all that is strange In the boundless realm of unending change." We have also, I think, to recognize an intermediate group of iivoni investigatora who, while; highly trained in :i morphological way, have shown abo a deep and 7 productive interest in the functional aspects of organ- ized nature, without, however, attaining the highest levels of achievement in thought on the dynamical side of medical research. In this category we may place Harvey, Malpighi, John Hunter, Johannes Miiller, Cohnheim and Robert Koch. And I think we may safety add that most modern investigators, educated under the influence of the strong trend to physiological thought, belong in this intermediate position. The examples of medical discovery which I shall first bring to your notice I shall select from the first and intermediate groups of workers, reserving the illustra- tions from the second group for subsequent considera- tion. The first great morphologist of modern times is Vesa- lius, whose claims to recognition rest not merely on his masterly and precise description of the parts of the human body, but also on his abrupt departure from the Galenic traditions and teachings, forced on him by the objectivity and sincerity of his studies. While we must regard the work of Vesalius as evidence of intellectual and logical power, it would be an error to credit him with the highest type of imagination or with elaborate esthetic reactions. The self-willed, clear-thinking man won his triumphs more by force of character and unswerving purpose than by creative intellect; and we see this type of worker repeated in some of our greatest modern anatomists, as also in some fields in which the experimental method is prominent. The idealism which inspired Vesalius was not proof against exasperations and discouragements due to the hostility of the Catholic church to all research on the human body. After destroying valuable manuscripts 8 and resigning his professorship, the great anatomist attached himself to the court of the Emperor Charles V and afterward to that of Philip II. But power and posi- tion and wealth did not repay him for the loss of intel- lectual freedom which such associations imposed, and for some reason he left Spain to visit the Holy Land. It is said that the pilgrimage was made in penance for an autopsy performed on a young woman not quite dead; and Edith Wharton has seized on the story to enrich her admirable Browning-like poem, "Vesalius in Zante" : The girl they brought me, pinioned hand and foot In catalepsy — say I should have known That trance had not yet darkened into death, And held my scalpel. Well, suppose I knew? Sum up the facts — her life against her death. Her life? The scum upon the pools of pleasure Breeds such by thousands. And her death? Perchance The obolus to appease the ferrying Shade, And waft her into immortality. Think what she purchased with that one heart-flutter That whispered its deep secret to my blade! Ah, no! The sin I sinned was mine, not theirs. Not that they sent me forth to wash away — None of their tariffed frailties, but a deed So far beyond their grasp of good or ill That, set to weigh it in the Church's balance, Scarce would they know which scale to cast it in. But I, I know. I sinned against my will, Myself, my soul, the God within the breast; Cm any penance w&ela such sacrilege? Bow vividly and how justly these verses paint the LOT86 that came from abandonment of ideals, when the young investigator, not yet thirty years of age, 9 exchanged the inner satisfaction of legitimate work for the prestige of courts ! But Vesalius in that short span of work had founded anatomy, and Eustaehius and Fallopius, his successors, united their influence with his (despite some disloyalties and antagonisms) to establish the scientific method in this branch of learning. The future of anatomy in Europe seemed assured. This gain in scientific method, initiated by Vesalius, was fixed and established in Eng- land by the spirited, penetrating and imaginative Wil- liam Harvey, whose monumental work proved that all the blood in the body travels in a circuit impelled by the beating of the heart. That a hugely skilled anat- omist should have made this physiological discovery is significant evidence that studies in structure may stimu- late a labile mind to serious investigation of the func- tional side of organic nature. Probably the work which Harvey did with his master, Fabricius, at Padua in the anatomy of the vascular system stimulated his interest in the discovery of experimental methods which should expose the true uses of this elaborate mechanism. And the same ingenuity which led to such conspicuous suc- cess in physiological research, the same interest in the vital phenomena, caused Harvey to ponder and study the mysteries of development in the chick, the deer and other mammals. These embryological observations are of such a grade of excellence that some of the greatest biologists regard them as superior in quality to the immortal studies of the circulation. The lofty intellect of Harvey was linked with a gen- erous and idealistic nature. His portraits show a forma- 10 tion of head and face that reminds us of representations of Shakespeare. Like Hunter and Darwin, he had the virtue of being extremely slow in publishing. He for- gave his man}' antagonists, notwithstanding the troubles they brought into his life. He says : I would not charge with wilful falsehood any one who was sincerely anxious for truth, nor lay it to any one's door as a crime that he had fallen into error. I am, myself, the partisan of truth alone; and I can indeed say that I have used all my endeavors, bestowed all my pains on an attempt to produce something that should be agreeable to the good, profitable to the learned, and useful to letters. More than a hundred years after the death of Harvey there emerged from obscurity a Scotchman, John Hun- ter, of such power and versatility as to make him a worthy intellectual successor of the great Englishman. We may take him as our second example of an investi- gator of our intermediate group, combining the interests of morphologist and physiologist. Of his works as anatomist and surgeon and comparative anatomist, I shall say nothing here. The wonderful Hunterian Museum of London is a peerless monument to the labors of the anatomist and surgeon. But it does not espe- cially direct our thoughts to his physiological and experi- mental way of thinking, which we may safely consider his strongest claims to greatness. One example — a cele- brated instance — will illustrate the point I wish to make. It was in Richmond Park that Hunter saw the deer irhose growing antlers awakened in his mind a singu- larly fruitful physiological question. What would hap- pen if he shut ofT the blood-supply of the antler on one 11 side by tying the corresponding carotid artery ? Experi- ment showed that the antler lost its warmth and ceased to grow; but for a short time only was there this check to growth. After a time the horn warmed again and grew. Had he failed to really obstruct the blood flow in the artery? No. Examination showed the carotid to have been securely ligated. Whence, then, came the blood essential for the antler's growth? Through the neighboring arteries that had grown distended, through what we now call the collateral circulation. So was the fact of the collateral circulation revealed. The thought- ful and logical mind of the practical surgeon soon found an important application of this discovery to human pathology. No one had dared to treat aneurism by liga- tion for fear of causing gangrene. But the existence of a collateral circulation held out a prospect of keeping the parts alive despite the ligation of an important artery. The first trial of the new method on a popliteal aneurism was successful, and the Hunterian operation, as you know it in surgery to-day, came into assured exist- ence. An unimaginative man could not have made this discovery in this manner. Yet Hunter belongs to the logical, independent, matter-of-fact type with fancy well controlled, rather than to the dreamers and poets of science. He was a rough diamond, with an intensely objective nature, and he had corresponding limitations. He is said to have rebelled against the classical teach- ings of Oxford. "Why, they wanted me to study Greek. They wanted to make an old woman of me!" And when twitted with his lack of knowledge of the "dead languages" he said of his critic: "I could teach him 12 that in the dead bod}" which he never knew in any lan- guage, living or dead.''* The idealism of Hunter showed itself in devotion to work and in fortitude in the advers- ity of ill health. 1 wish now to invite your attention to our second type of investigator — the essentially dynamical or physiologi- cal discoverer. The group, as I see it, is a small one. It includes Claude Bernard, Louis Pasteur, Hermann von Helmholtz and Paul Ehrlich. An admirer said sententiously of Bernard: "He is not merely a physiologist; he is physiology itself"; and the saying has the merit of reminding us of the breadth and depth and originality of his researches. With equal skill he worked at the physical and chemical bases of physiology; and we owe to him our knowledge of the glycogenic function of the liver, the enzymes of the pancreatic juice, the vasomotor system of nerves, diabetes from puncture of the fourth ventricle, besides many minor discoveries and researches and a masterly correla- tion of the general facts of animal and plant life. Ber- nard was one of the founders of modern pharmacology. He also foreshadowed in a singular manner and under singular circumstances the modern conception of soluble ferments in micro-organisms, a view which unfortun- ately brought him into an unpleasant antagonism with his life-long friend, Pasteur. The research that most fully shows the controlled imagination of Bernard is that which, extending over -. culminated in the discovery of the glycogenic function of the liver, a discovery of the very first signifi- e to physiology and pathology. We know the steps 16 which, led him to this discovery, and in retracing these steps we get an edifying glimpse of the workings of Bernard's fertile mind. His ambition was to follow the three great classes of foodstuffs, carbohydrates, fats and proteids, through the organism. He soon felt the neces- sity of limiting himself to the fate of the carbohydrates, which, besides seeming relatively simple to study, espe- cially attracted him on account of their mysterious rela- tion to diabetes. The first step in the research brought out the fact that cane-sugar, when acted on by gastric juice, undergoes a transformation which adapts it for absorption and utilization by the tissues — namely, a change into dextrose (glucose). He knew from the experiments of Tiedemann that starch is changed into dextrose in the digestive tract before absorption. Ber- nard asked himself what was the fate of this dextrose. He proposed to trace the course of the sugar from the digestive tract, along the portal vein to the liver, from the liver to the lungs by way of the right heart, and finally from the lungs through the left heart to the various tissues. His idea was that at one of these sta- tions the dextrose disappears, is destroyed or in some manner changed. "If I am able," said he, "to suppress the activity of this station, sugar will accumulate in the blood and a condition of diabetes will be brought about." Here, then, was a highly interesting enterprise. The first thing to do was to feed a dog freely on carbo- hydrates, kill it at the height of digestion and examine the blood leaving the liver by the hepatic veins to see if any sugar were lost in the liver. Please note that Ber- nard was helped in this search for sugar in the blood and 14 tissues by the cupric sulphate test for dextrose, just introduced by his friend, Barreswill — a very material help. Sugar was found in abundance in the blood of the hepatic veins ; therefore, the liver was not the looked-f or place of disappearance of dextrose. "But how do I know," thought Bernard, "that the sugar which I thus find in the hepatic vein is the same sugar as that which I introduced into the portal blood through the food?" To get an answer, Bernard fed a dog on meat only, knowing by experiment that no dextrose would then be present either in the digestive tract or in the portal blood. Then he examined the blood of the hepatic vein for sugar. Great was his surprise to find it loaded with dextrose. His keen intelligence at once drew the correct inference — that the liver is a sugar-making organ and makes sugar out of something which is not sugar, and, furthermore, that within the liver lies the secret of diabetes. Bernard now made a variety of experiments to test the correctness of his inferences. He soon found that sugar was contained in a simple decoction of the liver and that this sugar was dextrose, capable of fer- mentation and responding to all the known tests. But Bernard did not stop here. His fancy urged him to seek the substance in the liver from which the sugar is pro- duced — the "glycogenic substance" whose existence was inferred from experiment. And in time he isolated the substance which we know to-day as glycogen. Bere, then, was a great triumph of the experimental method in the hands of an imaginative, critical and highly skilled technical worker. The completeness with wlnVli the discovery at the glycogenic function of the 15 liver was worked out makes it a model of physiological research for all time. Moreover, the facts elicited by Bernard in this research possess a very broad bearing. They show that the liver has a function as important as, but far less obvious than, the secretion of bile — the first example of an internal secretion. And they prove that animals as well as plants can build up carbohydrate material — glycogen — by means of their own tissues. Finally Bernard very clearly showed that, while the production of glycogen from sugar is a vital act, in the sense of occurring only under conditions of life, the converse process, namely, the formation of sugar from glycogen, is independent of living tissues and may occur as the result of the action of a ferment in the blood. As Sir Michael Foster said most aptly : It is in the putting forth of the hypothesis that the true man of science shows the creative power which makes him and the poets brothers. His must be a sensitive soul, ready to vibrate to Nature's touches. Before the dull eye of the ordi- nary mind facts pass one after the other in long procession, but pass without effect, awakening nothing. In the eye of the man of genius, be he poet or man of science, the same facts light up an illumination, in the one of beauty, in the other of ti-uth; each possesses a responsive imagination. Such had Bernard, and the responses which in his youth found expres- sion in verses, in his maturer and trained mind took the form of scientific hypothesis. That Bernard well understood the value of imagina- tion in research and also its dangers is well shown by his admirable and memorable advice to his pupils : Put off your imagination as you take off your overcoat when you enter the laboratory; but put it on again, as you do your overcoat, when you leave the laboratory. Before the experi- 16 ment and between whiles, let your imagination wrap you round; put it right away from yourself during the experi- ment itself, lest it hinder your observing power. The dramatic and poetic instincts were strong in Ber- nard. He composed a vaudeville comedy called "The Eose of the Rhone," and later a metrical tragedy which he altered to a prose drama. But the love of analysis and of original research triumped over these esthetic tendencies of Bernard's nature, and in the reserved and inhibited personality and somewhat cold intellectuality of his maturer years it was not always easy to detect this underlying esthetic and emotional trait. His mar- ried life did not bring him happiness, as his wife sought display and material successes and was unable to under- stand the purity of purpose from which he never swerved in the long career to which physiology owes so great a debt. Let us dow bring to your attention some features of the mental life of another great physiologist, Hermann von Helmholtz, representing a very different phase of physiology from that developed by Bernard. Bernard, though accomplished as a morphologist and skilled in mechanical physiology, leaned strongly to the chemical side. He was essentially the animal experimentalist. Mathematics played only the most simple role in his researches. Helmholtz, on the other hand, approached physiology on its physical side, and, one may remark in passing, with a quality and amplitude of success unequalled before or since. He used the higher mathe- ni;iti<- constantly and they proved keen tools in his hands. Although an experimentalisl of the very first 17 order, Helmholtz was not an animal experimenter except in a very limited way, the nature of his themes making vivisection for the most part unnecessary. Even as a child the mind of Helmholtz was unconven- tional and inquiring, bent on understanding what was going on about him. The boy cut his own path through the mazes of unassimilable educational offerings. His tastes were definite. He obtained notions of geometry from the blocks with which he played, surprised his mother by experimenting on her linen with acids, made telescopes with spectacle lenses, read books on physics and enjoyed greatly his walks in the country. At the university he assimilated ideas with great ease and showed an increasing interest in physics, which he wished to follow as a profession. But his prudent father urged him to study medicine as a surer means of liveli- hood. And most fortunate it was for medical science that the gifted young man was willing to take up medi- cal studies, for there arose in him a deep interest in the problems of physiology, destined to bear rich fruit. The duties of an army surgeon took only part of his time and the rest he gave to physics. His original researches began at the age of 21 and continued through a long lifetime, covering an extraordinary range of topics in an original and masterly way. Helmholtz contributes to minute anatomy, lays the foundations of physiological optics and acoustics (with all that this means for esthetics, psychology and metaphysics), gives to medi- cine the specific and golden gift of the ophthalmoscope, enriches physics with an imperishable statement of the doctrine of the conservation of energy and with original 18 studies on vortex motion, on hydrodynamics, on electro- dynamics, on dynamics, on meteorological physics. He broadens chemical theory by the influence of his vortex motion hypothesis and, in a somewhat incidental way, brings new theoretical conceptions into the realm of pure mathematics. As students of the psychical forces that have fertilized modern medicine it is interesting for us to note that Helmholtz disclaimed any intention to be practical in his work. If the themes that happened to absorb his attention led to practical and humanely useful results, he was pleased; but he seldom pursued a practical aim simply because of its utility. He chose his themes because they promised to be intellectually satisfying, giving little heed to the nature of the prob- able outcome. He framed his experiments so that Xature would have to answer "Yes" or "No" to his questions, thus furnishing him with definite results. The story of the invention of the ophthalmoscope illustrates the mental processes of Helmholtz in working out an idea. He did not set out to devise an instrument for studying the retina and the ocular refraction, but as he proceeded these important possibilities ripened into definite objects. He says : I was endeavoring to explain to my pupils the emission of reflected light from the eye, a discovery made by Brlicke, who would have invented the ophthalmoscope had he only asked himself how an optical image is formed by the light returning from the eye. In his research it was not necessary to ask it, but had he asked it, he was just the man to answer it as quickly at I did, and to invent the instrument. I turned the problem over and over t<> ascertain the simplest way in which to demonstrate the phenomenon to my students. It was also 10 a reminiscence of my days of medical study, that ophthal- mologists had great difficulty in dealing with certain cases of eye disease, then known as black cataract. The first model was constructed of pasteboard, eye lenses, and cover-glasses used in the microscopic work. It was at first so difficult to use that I doubt if I should have persevered, unless I had felt that it must succeed; but in eight days I had the great joy of being the first who saw before him a human retina. The basis for this invention was Helmsholtz's knowl- edge of the anatomy of the eye, his mastery of physio- logical optics, his experimental ability, and, as stated in his own language, his wise to devise an improved method of demonstrating a somewhat obscure phe- nomenon to his students. Modesty and generous impulse made Helmholtz say that Brucke could equally well have invented the ophthalmoscope had he only asked himself how an optical image is formed by the light returning from the eye. I doubt if it could be successfully contended that Briieke's actual information about the eye was less than Helmholtz's. Helmholtz himself says that Brucke "was just the man" to make the invention, and by this he must refer to equipment in knowledge. In what, then, did Helmholtz excel Brucke ? I would answer, in creative fancy, in imagination. The controlled play of fancy, using the facts of the case for its playground, is what made Helmholtz see the possi- bilities and sec them so clearly as also to make it appear worth while to put energy into the effort to see the retina. It would be easy to multiply examples of the almost playful way in which Helmholtz utilized the children of his rich fancy to extend the bounds of scientific knowl- 20 edge. The ease with which he made his intellectual progress is one of the most striking features of his won- derfully creative career. Often on solitary walks in the country he experienced ideas that seemed to clarify refractory problems. From the great wealth of his impressions and associated ideas, arising through the operation of active fancy or imagination, there seems to have been a process of controlled selection and rejection by which the finished products, the great ideas, were built up — a conscious selection not without analogies to natural selection in the upbuilding of the physical machinery. In the entire list of the masters of medicine I think there has been only one mind that can be regarded as belonging on the same lofty level as that of Helmholtz, in respect to controlled yet expansive powers of imagination combined with the energy of performance and the technical training necessary to apply those powers. The intellect of Pasteur, and his alone, has revealed associative power and logical sequences of thought culminating in discoveries fairly comparable to those of Helmholtz in respect to the depth of their psychical basis. And it is probably no accident that the two greatest minds in medicine have entered it on the streams of pure science, Helmholtz as the biological physicist, Tasteur as the biological chemist. As a human being Helmholtz takes rank with the noblest of men. Considerateness for others and a will- ingness to help worthy persons were prominent charac- teristic. He had a calm self-control which still left him QAtnral and simple in human relations, although tdi- fine dignit] served Be ;i check to the approaches of 21 shallow and trivial people. Helmholtz was an idealist of the purest type, and never permitted personal inter- est to interfere with his best aims as a student of science. His was a poetic nature, apt in versification and in music, yet with an intellect so searching that he was not entirely satisfied by esthetic feeling and phantasy, but sought also to understand them. Modesty was one of his greatest charms, and this quality was attractively seen in the sentiment which he expressed on being awarded the von Graefe medal in recognition of his services to medicine through the invention of the ophthalmoscope : Let us suppose that up to the time of Phidias nobody has had a chisel sufficiently hard to work on marble. Up to that time they would only mold clay or carve wood. But a clever smith discovers how a chisel can be tempered. Phidias rejoices over the improved tools, fashions with them his god-like statues and manipulates the marble as no one has ever before done. He is honored and rewarded. But great geniuses are modest just in that in which they most excel others. That very thing is so easy for them that they can hardly under- stand why others cannot do it. But there is always associated with high endowments a correspondingly great sensitiveness for the defects of one's own work. Thus, says Phidias to the smith, "Without your aid I could have done nothing of that; the honor and glory belong to you." But the smith can only answer him, "But I could not have done it even with my chisels, whereas you, without my chisels, could at least have molded your wonderful works in clay; therefore I must decline the honor and glory, if I will remain an honorable man." But now Phidias is taken away, and there remain his friends and pupils — Praxiteles, Paionios, and others. They all use the chisel of the smith. The world is filled with their work and their fame. They determine to honor the memory of the deceased with a garland which he shall receive who has done 22 the most for the art, and in the art, of statuary. The beloved master has often praised the smith as the author of their great sucess, and they finally decide to award the garland to him. "Well," answers the smith, "I consent; you are many, and among you are clever people. I am but a single man. You assert that I singly have been of service to many of you, and that many places teem with sculptors who have decked the temples with divine statutes, which, without the tools that I have given you, would have been very imperfectly fashioned. I must believe you, as I have never chiseled marble, and I accept thankfully what you award to me, but I myself would have given my vote to Praxiteles or Paionios." If we turn now to Helmholtz's great contemporary, Louis Pasteur, we discern many points of resemblance in the mental endowments and in the careers of these two superlatively eminent masters of medical science. Pasteur, like Helmholtz, was greatly helped in early life by the patient guidance of earnest and capable parents, and, like him, showed a strong interest in poetry and art, the portraits made by Pasteur during his teens showing unmistakable artistic talent. Pasteur's considerable aptitude for mathematics developed later than tbat of Helmholtz and was of a less original sort, yet served him well, especially in his earlier researches. Both men were endowed with phantasy and associative power of the highest order, but, while Helmholtz seldom departed from the path of strict logical development of his ideas, Pasteur, with his more impetuous nature, -ometimes permitted himself to make speculative excur- sions of a more random kind. Both found their great- est enjoyment in dealing with the development of gen- eral ideas, but Pasteur, on realizing his power to help mankind through his discoveries, deliberately turned his 28 rare gifts to the solution of practical problems in medi- cine, whereas Helmholtz was satisfied to continue to build the foundations for the physiology of the sense organs and for a better psychology and metaphysics. It is very noteworthy that both Helmholtz and Pasteur were deeply influenced in their outlook by certain con- ceptions of wide applicability. Helmholtz learned from his great master, Johannes Miiller, to attach great importance to the principle of the specificity of nerves — that is, the doctrine which teaches that nerves of special sense, as the optic or acoustic nerves, however stimu- lated, respond with a quite specific reaction, with sensa- tions of light or sensations of sound, respectively. This principle guided Helmholtz not alone in his studies of the physiology of the special senses, but in his philo- sophical attitude, which brought him into collision with the widely accepted metaphysics of Kant. On the other hand, Pasteur's scientific and philosophical thought was influenced definitely and profoundly by the conception of molecular asymmetry in nature. His interest in this subject was awakened by the study of the salts of tar- taric acid, which culminated in 1848 with the famous discovery that the optically indifferent or racemic tar- taric acid crystallizes into equal quantities of the ordi- nary dextrorotary tartaric acid and of the newly recog- nized levorotary tartaric acid. It was Pasteur's interest in the problem of molecular asymmetry, and especially certain theoretical notions on which we need not linger here, that induced him to experiment on the action of micro-organisms on racemic ammonium tartrate, with the striking result that the living beings converted the 24 optically indifferent solution of salts into a levorotary solution. This showed that the dextrorotary constituent of the indifferent raceniic tartrate had been assimilated by the micro-organisms, while the levorotary constituent was unaffected. I emphasize these studies of Pasteur's because they were what excited his interest in the then obscure problem of fermentation, which in turn led him to take up those studies of the causation of disease by micro-organisms and those researches on immunity which have revolutionized the entire science and art of medicine. To do anything like justice to these extraor- dinarily fertile and original researches of Pasteur is wholly out of question here. I can merely direct your attention to the researches which in the fullest way exemplify Pasteur's gift of imagination and power of experimental control. There are six studies or groups of studies whose histories exhibit Pasteur's genius at its best — the research on the tartrates, the investigations on fermentation, the inquiry into the causes of the silk- worm disease, and the methods of its eradication, the research on chicken cholera and immunity to it, the research on anthrax, with the extraordinarily dramatic scenes attending the public test of the immunization methods, and finally the masterly researches on hydro- phobia. People have, in general, been perhaps most impressed by the researches on hydrophobia. Here Pas- teur dealt intimately with a disease affecting man. The orrible effects of rabies on liuman personality, the pub- lish of the ftret daring attempts at prevention by the • ,'i attenuated virus, the personal activity and earn- estness of Pas-t '-u r in lln-v lium.ui < .|i