An Introduction to the Study of Experimental Medicine

We said, on the other hand, that man would never know either the primary cause, nor the essence of things. Hence truth never shows itself to his mind except in the form of a connection or of a necessary and absolute relation. But this connection may be absolute only in so far as its conditions are siniple and subjective, that is, when the mind is aware of knowing them all. Mathematics embodies the relations of things in conditions of ideal simplicity. It follows that these principles or relations, once found, are accepted by the mind as absolute truths, i.e., truths independent of reality. We see now that all logical deductions in a piece of mathematical reasoning are just as certain as their principle, and that they do not require verification by experiment. That would be trying to place the senses above reason ; and it would be absurd to seek to prove what is absolutely true for the mind and what it could not conceive otherwise.

But when man stops working with subjective relations, the conditions of which his mind has created, and tries to learn about the objective relations of nature which he has not created, then at once the inner and conscious criterion fails him. He is, of course, still aware that in the objective or outer world truth consists, in the same way, of necessary relations ; but he lacks knowledge of the conditions of these relations. Only if he had created these conditions, indeed, could he possess absolute knowledge of them and absolute understanding.

Still man must believe that the objective relations between phenomena of the outer world might attain the certainty of subjective truths if they were reduced to a state of simplicity that his mind could completely grasp. Thus, in the study of the simplest of natural phenomena, experimental science has laid hold on certain relations which appear absolute. Such are the propositions which serve as principles in theoretical mechanics and in some branches of mathematical physics. In these sciences, indeed, we reason by logical deduction which we do not submit to experiment, because we admit, as in mathematics, that the principle being true the deductions are

true also. Still, there is a wide difference to note in this respect, that the starting point here is no longer a subjective and conscious truth, but an objective and unconscious truth, borrowed from observation or experiment. Now this truth is never more than relative to the number of experiments and observations that have been made. Even if no observation has so far disproved the truth in question, still the mind does not therefore imagine that things cannot happen otherwise; so that it is only by hypothesis that we admit the principle as absolute. That is why the application of mathematical analysis to natural phenomena, even very simple ones, may have its dangers if experimental verification is. entirely rejected. In this case, mathematical analysis becomes a blind instrument, if we do not from time to time retemper it in the furnace of experiment. I here express a thought uttered by many great mathematicians and great physicists ; and in order to recall one of the most authoritative opinions in this field, I will cite what my learned associate and friend, J. Bertrand, wrote on this subject in his fine tribute to Senarmont: ^'For the physicist, geometry should be only a powerful ally: when it has pushed its principles to their last consequences, it can do no more, and the uncertainty of the starting point can only be increased by the blind logic of analysis, if experiment at each step does not serve as compass and ruler." ^

Theoretical mechanics and mathematical physics make the connection then between mathematics proper and the experimental sciences. They include the simplest cases. But as soon as we go into physics and chemistry, and especially biology, the phenomena are complicated by so many relations that the principles, embodied in theories to which we have been able to rise, are only provisional and are so hypothetical that our deductions, even though very logical, are absolutely uncertain and can in no case dispense with experimental verification.

In short, man may relate all his reasonings to two criteria: the one, inner and conscious, is sure and absolute; the other, outer and unconscious, is experimental and relative. When we reason about outer objects, but consider them in their relation to ourselves according to the pleasure or displeasure which they occasion us in proportion to their utility or their disadvantages, * J. Bertrand, Eloge de M. Senarmont, address given at the sixth annual public meeting of the 8oci4t4 de seoours des amis des sciences.

we still possess an inner criterion in our sensations. So, when we reason about our own actions, we again have a sure guide, because we are conscious of what we are thinking and of what we are feeling. But if we wish to judge the actions of another man and to know the motives which make him act, then it is quite different. Doubtless we see before our eyes the man's movements and the acts which, we are sure, are expressions of his feeling and his will. What is more, we also admit that there is a necessary relation between actions and their cause ; but what is this cause ? We do not feel it ourselves, we are not aware of it as in our own case ; we are therefore forced to interpret and imagine it from the movements that we see and the words that we hear. So we must verify the man's acts, one by another; we consider how he behaves in such and such circumstances, and in short, we turn to the experimental method. In like manner, when a man of science considers the natural phenomena which surround him and which he wishes to know in themselves and in their complex mutual relations of causation, every inner criterion fails him, and he is forced to invoke experiment to verify the suppositions and the reasonings that he is making about them. Experiment, then, according to Goethe's expression, becomes the one mediator between the objective and the subjective,^ that is to say, between the man of science and the phenomena which surround him.

Experimental reasoning is the only reasoning that naturalists and physicians can use in seeking the truth and approaching it as nearly as possible. Indeed, in its very character as an outer and unconscious criterion, experiment gives only relative truth, without being able to prove to the mind that it knows truth absolutely. An experimenter facing natural phenomena is like a spectator watching a dumb show. He is in some sort the examining magistrate for nature ; only instead of grappling with men who seek to deceive him by lying confessions or false witness, he is dealing with natural phenomena which for him are persons whose language and customs he does not know, persons living in the midst of circumstances unknown to him, yet persons whose designs he wishes to learn. For this purpose he uses all the means within his power. He observes their actions, their gait, their behavior, and he seeks to disengage their cause by means of various attempts, called experiments. He

* Goethe, CEuvres d'histoire naturelle, translation by M. Ch. Martins, Introduction, p. 1. uses every imaginable artifice, and, as the popular expression goes, he often makes a false plea in order to learn the truth. In all this, the experimenter reasons necessarily according to his own character and lends to nature his own ideas. He makes suppositions about the cause of actions taking place before his eyes ; and to learn whether the hypothesis which serves as groundwork for his interpretation is correct, he takes measures to make facts appear which in the realm of logic may be either the confirmation or the negation of the idea which he has conceived. Now, I repeat, only this logical verification can teach him and give him experience. The naturalist observing animals whose behavior and habits he wishes to know, the physiologist and the physician wishing to study the hidden functions of living bodies, the physicist and the chemist defining the phenomena of inert matter, — they are all in the same situation; they have manifestations before them which they can interpret only with the help of the experimental criterion, the only one which we need to consider here.

We said above that the experimental method rests successively on feeling, reason and experiment. Feeling gives rise to the experimental idea or hypothesis, i.e., the previsioned interpretation of natural phenomena. The whole experimental enterprise comes from the idea, for this it is which induces experiment. Reason or reasoning serves only to deduce the consequences of this idea and to submit them to experiment. An anticipative idea or an hypothesis is, then, the necessary starting point for all experimental reasoning. Without it, we could not make any investigation at all nor learn anything; we could only pile up sterile observations. If w^e experimented without a preconceived idea, we should move at random, but, on the other hand, as we have said elsewhere, if we observed with preconceived ideas, we should make bad observations and should risk taking our mental conceptions for reality.

Experimental ideas are by no means innate. They do not arise spontaneously; they must have an outer occasion or stimulant, as is the case in all physiological functions. To have our first idea of things, we must see those things; to have an idea about a natural phenomenon, we must, first of all, observe it. The mind of man cannot conceive an effect without a cause, so that the sight of a phenomenon always awakens an idea of causation. All human knowledge is limited to working back from observed effects to their cause. Following an observation, an idea connected with the cause of the observed phenomenon presents itself to the mind. We then inject this anticipative idea into a train of reasoning, by virtue of which we make experiments to control it.

Experimental ideas, as we shall later see, may arise either a 'priori of a fact observed by chance or following some experimental venture or as corollaries of an accepted theory. For the moment, we may merely note that the experimental idea is by no means arbitrary or purely imaginative; it must always have a support in observed reality, that is to say, in nature. The experimental hypothesis, in short, must always be based on prior observation. An- other essential of any hypothesis is that it must be as probable as may be and must be experimentally verifiable. Indeed if we made an hypothesis which experiment could not verify, in that very act we should leave the experimental method to fall into the errors of the scholastics and makers of systems.

A propos of a given observation, no rules can be given for bringing to birth in the brain a correct and fertile idea that may be a sort of intuitive anticipation of successful research. The idea once set forth, we can only explain how to submit it to the definite precepts and precise rules of logic from which no experimenter may depart; but its appearance is wholly spontaneous, and its nature is wholly individual. A particular feeling, a quid proprium constitutes the originality, the inventiveness, or the genius of each man. A new idea appears as a new or unexpected relation which the mind perceives among things. All intellects doubtless resemble each other, and in all men similar ideas may arise in the presence of certain simple relations between things, which everyone can grasp. But like the senses, intellects do not all have the same power or the same acuteness ; and subtle and delicate relations exist which can be felt, grasped and unveiled only by minds more perceptive, better endowed, or placed in intellectual surroundings which predispose them favorably.

If facts necessarily gave birth to ideas, every new fact ought to beget a new idea. True, this is what most often takes place ; for new facts exist, the character of which makes the same new idea come to all men, placed in the same circumstances as respects previous information. But facts also exist which mean nothing to most minds, while they are full of light for others. It even happens that a fact or an observation stays a very long time under the eyes of a man of science without in any way inspiring him; then suddenly there comes a ray of light, and the mind interprets the fact quite differently and finds for it wholly new relations. The new idea appears, then, with the rapidity of lightning, as a kind of sudden revelation; which surely proves that in this case the discovery inheres in a feeling about things which is not only individual, but which is even connected with a transient condition of the mind. The experimental method, then, cannot give new and fruitful ideas to men who have none; it can serve only to guide the ideas of men who have them, to direct' their ideas and to develop them so as to get the best possible results. The idea is a seed; the method is the earth furnishing the conditions in which it may develop, flourish and give the best of fruit according to its nature. But as only what has been sown in the ground will ever grow in it, so nothing will be developed by the experimental method except the ideas submitted to it. The method itself gives birth to nothing. Certain philosophers have made the mistake of according too much power to method along these lines.

The experimental idea is the result of a sort of presentiment of the mind which thinks things will happen in a certain way. In this connection we may say that we have in our minds an intuition or feeling as to the laws of nature, but we do not know their form. We can learn it only from experiment. Men with a presentiment of new truths are rare in all the sciences ; most men develop and follow the ideas of a few others. Those who make discoveries are the promoters of new and fruitful ideas. We usually give the name of discovery to recognition of a new fact ; but I think that the idea connected with the discovered fact is what really constitutes the discovery. Facts are neither great nor small in themselves. A great discovery is a fact whose appearance in science gives rise to shining ideas, whose light dispels many obscurities and shows us new paths. There are other facts which, though new, teach us but little ; they are therefore small discoveries. Finally, there are new facts which, though well observed, teach nothing to any-

one; they remain, for tlie moment, detaclied and sterile in science; they are what we may call raw facts or crude facts. Discovery, then, is a new idea emerging in connection with a fact found by chance or otherwise. Consequently, there can be no method for making discoveries, because philosophic theories can no more give inventive spirit and aptness of mind to men, who do not possess them, than knowledge of the laws of acoustics or optics can give a correct ear or good sight to men deprived of them by nature. But good methods can teach us to develop and use to better purpose the faculties with which nature has endowed us, while poor methods may prevent us from turning them to good account. Thus the genius of inventiveness, so precious in the sciences, may be diminished or even smothered by a poor method, while a good method may increase and develop it. In short, a good method promotes scientific development and forewarns men of science against those numberless sources of error which they meet in the search for truth; this is the only possible object of the experimental method. In biological science, the role of method is even more important than in other sciences, because of the immense complexity of the phenomena and the countless sources of error which complexity brings into experimentation. Yet even from the biological point of view, we cannot claim to treat the experimental method completely here ; we must limit ourselves to giving a few general principles for the guidance of minds applying themselves to research in experimental medicine.

III. Experimenters Must Doubt, Avoid Fixed Ideas, and Always Keep Their Freedom of Mind The first condition to be fulfilled by men of science, applying themselves to the investigation of natural phenomena, is to maintain absolute freedom of mind, based on philosophic doubt. Yet we must not be in the least sceptical ; we must believe in science, i.e., in determinism; we must believe in a complete and necessary relation be^ tween things, among the phenomena proper to living beings as well as in all others; but at the same time we must be thoroughly convinced that we know this relation only in a more or less approximate way, and that the theories we hold are far from embodying changeless truths. When we propound a general theory in our sciences,

we are sure only that, literally speaking, all such theories are false. They are only partial and provisional truths which are necessary to us, as steps on which we rest, so as to go on with investigation ; they embody only the present state of our knowledge, and consequently they must change with the growth of science, and all the more often when sciences are less advanced in their evolution. On the other hand, our ideas come to us, as we said, in view of facts which have been previously observed and which we interpret afterward. Now countless sources of error may slip into our observations, and in spite of all our attention and sagacity, we are never sure of having seen everything, because our means of observation are often too imperfect. The result of all this is, then, that if reasoning guides us in experimental science, it does not necessarily force its deductions upon us. Our mind can always remain free to accept or to dispute these deductions. If an idea presents itself to us, we must not reject it simply because it does not agree with the logical deductions of a reigning theory. We may follow our feelings and our idea and give free rein to our imagination, as long as all our ideas are mere pretexts for devising new experiments that may supply us with convincing or unexpected and fertile facts.

The freedom which experimenters maintain is founded, as I said, on philosophic doubt. Indeed, we must be aware of the uncertainty of our reasonings on account of the obscurity of their starting point. The starting point, fundamentally, always rests on hypotheses or theories more or less imperfect, according to the state of development of the sciences. In biology, and especially in medicine, theories are so precarious that the experimenter maintains almost all his freedom. In chemistry and physics the facts are simpler, the sciences are more advanced, the theories more secure, and the experimenter must take more account of them and allow greater importance to the deductions of experimental reasoning based on them. But still he must never accept these theories at their face value. In our day, we have seen great physicists make discoveries of the first rank by means of experiments devised in a way that lacked all logical relation to admitted theories. Astronomers have enough confidence in the principles of their science to build up mathematical theories with them, but that does not prevent them from testing and verifying them by direct observations ; this very precept, as we have seen, must not be neglected in theoretical mechanics. But in mathe-

matics, when we start from an axiom or principle whose truth is absolutely necessary and conscious, freedom no longer exists ; truths once established are immutable. Geometricians are not free to question whether the three angles of a triangle are or are not equal to two right angles ; consequently they are not free to reject the logical consequences deduced from this principle. If a doctor imagined that his reasoning had the value of a mathematician's, he would be utterly in error and would be led into the most unsound conclusions. This is unluckily what has happened and still happens to the men whom I shall call systematizers. These men start, in fact, from an idea which is based more or less on observation, and which they regard as an absolute truth. They then reason logically and without experimenting, and from deduction to deduction they succeed in building a system which is logical, but which has no sort of scientific reality. Superficial persons often let themselves be dazzled by this appearance of logic; and discussions worthy of ancient scholasticism are thus sometimes renewed in our day. The excessive faith in reasoning, which leads physiologists to a false simplification of things, comes, on the one hand, from ignorance of the science of which they speak, and, on the other hand, from lack of a feeling for the complexity of natural phenomena. That is why we sometimes see pure mathematicians, with very great minds too, fall into mistakes of this kind ; they simplify too much and reason about phenomena as they construct them in their minds, but not as they exist in nature.

The great experimental principle, then, is doubt, that philosophic doubt which leaves to the mind its freedom and initiative, and from which the virtues most valuable to investigators in physiology and medicine are derived. We must trust our observations or our theories only after experimental verification. If we trust too much, the mind becomes bound and cramped by the results of its own reasoning; it no longer has freedom of action, and so lacks the power to break away from that blind faith in theories which is only scientific superstition.

It has often been said that, to make discoveries, one must be ignorant. This opinion, mistaken in itself, nevertheless conceals a truth. It means that it is better to know nothing than to keep in mind fixed ideas based on theories whose confirmation we constantly seek, neglecting meanwhile everything that fails to agree with them. Nothing could be worse than this state of mind; it is the very opposite of inventiveness. Indeed a discovery is generally an unforeseen relation not included in theory, for otherwise it would be foreseen. In this respect, indeed, an uneducated man, knowing nothing of theory, would be in a better attitude of mind; theory would not embarrass him and would not prevent him from seeing new facts unperceived by a man preoccupied with an exclusive theory. But let us hasten to say that we certainly do not mean to raise ignorance into a principle. The better educated we are and the more acquired information we have, the better prepared shall we find our minds for making great and fruitful discoveries. Only we must keep our freedom of mind, as we said above, and must believe that in nature what is absurd, according to our theories, is not always impossible.

Men who have excessive faith in their theories or ideas are not only ill prepared for making discoveries; they also make very poor observations. Of necessity, they observe with a preconceived idea, and when they devise an experiment, they can see, in its results, only a confirmation of their theory. In this way they distort observation and often neglect very important facts because they do not further their aim. This is what made us say elsewhere that we must never make experiments to confirm our ideas, but simply to control them ; ^ which means, in other terms, that one must accept the results of experiments as they come, with all their unexpectedness and irregularity.

But it happens further quite naturally that men who believe too firmly in their theories, do not believe enough in the theories of others. So the dominant idea of these despisers of their fellows» is to find others' theories faulty and to try to contradict them. The difficulty, for science, is still the same. They make experiments only to destroy a theory, instead of to seek the truth. At the same time, they make poor observations, because they choose among the results of their experiments only what suits their object, neglecting whatever is unrela;ted to it, and carefully setting aside everything which might tend toward the idea they wish to combat. By these two opposite roads, men are thus led to the same result, that is, to falsify science and the facts.

• Claude Bernard, LeQons sur lea propriet6s et les alterations desf Uquides de Vorganisme. Paris, 1859, Premiere legon. Accordingly, we must disregard our own opinion quite as much as the opinion of others, when faced hy the decisions of experience. If men discuss and experiment, as we have just said, to prove a preconceived idea in spite of everything, they no longer have freedom of mind, and they no longer search for truth. Theirs is a narrow science, mingled with personal vanity or the diverse passions of man. Pride, however, should have nothing to do with all these vain disputes. When two physiologists or two doctors quarrel, each to maintain his own ideas or theories, in the midst of their contradictory arguments, only one thing is absolutely certain : that both theories are insufficient, and neither of them corresponds to the truth. The truly scientific spirit, then, should make us modest and kindly. We really know very little, and we are all fallible when facing the immense difficulties presented by investigation of natural phenomena. The best thing, then, for us to do is to unite our efforts, instead of dividing them and nullifying them by personal disputes. In a word, the man of science wishing to find truth must keep his mind free and calm, and if it be possible, never have his eye bedewed, as Bacon says, by human passions.

In scientific education, it is very important to differentiate, as we shall do later, between determinism which is the absolute principle of science, and theories which are only relative principles to which we should assign but temporary value in the search for truth. In a word, we must not teach theories as dogmas or articles of faith. By exaggerated belief in theories, we should give a false idea of science; we should overload and enslave the mind, by taking away its freedom, smothering its originality and infecting it with the taste for systems.

The theories which embody our scientific ideas as a whole are, of course, indispensable as representations of science. They should also serve as a basis for new ideas. But as these theories and ideas are by no means immutable truth, one must always be ready to abandon them, to alter them or to exchange them as soon as they cease to represent the truth. In a word, we must alter theory to adapt it to nature, but not nature to adapt it to theory. To sum up, two things must be considered in experimental science : method and idea. The object of method is to direct the idea which arises in the interpretation of natural phenomena and in the search for truth. The idea must always remain independent, and we must

no more chain it with scientific beliefs than with philosophic or religious beliefs ; we must be bold and free in setting forth our ideas, must follow our feeling, and must on no account linger too long in childish fear of contradicting theories. If we are thoroughly steeped in the principles of the experimental method, we have nothing to fear; for, as long as the idea is correct, we gO' on developing it ; when it is wrong, experimentation is there to set it right. We must be able, then, to attack questions even at the risk of going wrong. We do science better service, as has been said, by mistakes than by confusion, which means that we must fearlessly push ideas to their full development, provided that we regulate them and are always careful to judge them by experiment. The idea, in a word, is the motive of all reasoning, in science as elsewhere. But everywhere the idea must be submitted to a criterion. In science the criterion is the experimental method or experiment; this criterion is indispensable, and we must apply it to our own ideas as well as to those of others.

From all that has so far been said, it follows necessarily, that no man's opinion, formulated in a theory or otherwise, may be deemed to represent the whole truth in the sciences. It is a guide, a light, but not an absolute authority. The revolution which the experimental method has effected in the sciences is this: it has put a scientific criterion in the place of personal authority. The experimental method is characterized by being dependent only on itself, because it includes within itself its criterion, — experience. It recognizes no authority other than that of facts and is free from personal authority. When Descartes said that we must trust only to evidence or to what is sufficiently proved, he meant that we must no longer defer to authority, as scholasticism did, but must rely only on facts firmly established by experience.

The result of this is that when we have put forward an idea or a theory in science, our object must not be to preserve it by seeking everything that may support it and setting aside everything that may weaken it. On the contrary, we ought to examine with the greatest care the facts which apparently would overthrow it, because real progress always consists in exchanging an old theory which includes fewer facts for a new one which includes more. This proves that we have advanced, for in science the best precept is to alter and exchange our ideas as fast as science moves ahead. Our ideas are only intellectual instruments which we use to break into phenomena; we must change them when they have served their purpose, as we change a blunt lancet that we have used long enough.