Medical logic

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Preface

The purpose which this work is intended to fulfil is more fully explained in the Introduction. I shall therefore only say here as much as is necessary to obviate, at the outset, a misunderstanding to which its title might give rise. It can scarcely be necessary, indeed, to assure the reader that Logic, in its ordinary signification, is not here meant, but only the application of certain rules and principles of logic to the study of natural science in general, and of medicine in particular. Our aim, therefore, is a purely practical one — viz., to show, clearly and impressively, the mode in which we must proceed in our observations, investigations, and conclusions, in order that our Theorems and Problems may become more clearly intelligible, and that we may arrive at experimental truths and definite laws in our department of science, as well as at scientific principles of practice.

The methods and paths by which alone we can arrive at all these ends, and the technical details and peculiarities which encumber them in a study such as ours, have nowhere been set forth, or at least not so that the philosopher, or physician, could derive from them all the advantages and services which he requires at every step : for philosophers and professed logi-

Tiii PREFACE.

cians have seldom or never touched upon what we have most stood in need of, perhaps because the subject matter — the individual questions and objects with which the natural philosopher or physician has to deal — were not sufficiently familiar to them. The latter, on the other hand, seem often not to have closely considered or understood all the processes which they have themselves adopted in their investigations and operations, and by the aid of which they themselves have perhaps arrived, not only at their deductions and theories, but also at their most important discoveries. In short — many considerations have concurred to prove that Logic has not always so harmonized and entered into combination with Medicine, or Natural History, as is indispensably necessary for the interests of science. It would seem to me, that philosophy and logic have, on the one hand, by no means given us the precise aid which we require ; and that, on the other, we have not always sought for the support and guidance of a sound logic, where we could scarcely advance safely without it. We may, perhaps, have learnt philosophy, but not to philosophize — we may have learnt logic, but not to form correct opinions and conclusions from observation and investigation.

But since medicine and the study of natural philosophy have begun to assume a closer relation to each other, and physicians have engaged more frequently in scientific inquiries, and advanced from the field of mere empiricism and conjecture to that of comprehension and induction, the desire for scientific methods of inquiry and adequate demonstration has everywhere grown jipon them, and has thereby become a trustworthy guide. Men speak more frequently than heretofore of the necessity of a logical mode of proceeding, of a

PREFACE. ix

correct process of induction^ &c. ; but we have nowhere attained a distinct and complete understanding of all that which we presuppose^ nor have we learnt how to search and investigate in ovir department of science, so as most quickly to arrive at safe principles and conclusions.

The present has seemed to me, therefore, a seasonable and worthy attempt whereon to venture so far as my powers admit. And the hope of doing some service to my professional brethren, and, through them, to medicine, or even to natural science in general, has been increased by the circumstance that a period of calm research, in which facts have accumulated, has arrived, free from the excitement which new theories and systems usually produce. The most favorable moment has thus, perhaps, arrived, for making a psychical analysis of the general progress of the human mind; for observing the mind itself in the act of investigation, as well as the mode in which it investigates; and for inquiring why we have hitherto made no further advances in our department of science, and how we may, with the greatest degree of certainty, do so.

At this point, however, I wish to obviate the suspicion that the following pages contain nothing more than a pretended elucidation of ideas, and a critique, or that they wiU sweep away the past and leave only a " tabula rasa" for future investigators. The entire aim of this work is rather to endeavour to promote improvement and progress, than to overthrow, or to undo ; nor am 1 called upon to become the judge of my predecessors or contemporaries. It is with results only that we have here to deal, as our progress towards improvement — our future success — depends upon a clearer insight into any

X PREFACE.

deficiencies in these results, and especially into the causes of such deficiencies or errors,

If even a Bacon quoted himself as an instance that as a tyro in philosophy one can do much service, much more may a similar excuse be admitted for the author of this work, if his attempt should not fulfil the expectations of his readers. But it is always a difficult task to cement together the detached fragments of a subject never yet treated as a whole. It is, however, consolatory to bear in mind, that " he who cannot go to Palestine may still go to Rome," and thus have I, who am self-taught, endeavoured to weigh as exactly and carefully as possible for myself, and^^ to explain, in a manner free from the garb of scholastic philosophy, what has appeared to me to be at once most important and most difficult. Moreover, my guides have been " special," that is, men who have been engaged in one particular study, philosophers on the one hand, as well as naturalists and physicians, both of ancient and modern times, on the other. I am indebted, however, to J. Stuart Mill's excellent work for the greater part, the true pith and thread of my system, and the following is, in a great measure, but an application of his doctrines to the particular questions and objects of our department of science.

Oesterlen.

Heidelberg ; September, 1852.

Contents

PAGE

Section I

Medical Problems in a logical point of view, e. c, in reference to the possibility of solving them. — Topics and Questions with which Logic has to deal, both as a Science and as an Art . . . .31

Section II

Of the Methods and Means in general, by which the Naturalist, and especially the Physician, endeavours to attain a perception of Natural Phenomena and Processes, from the study of their Conditions and Laws . . 40

Section III

On the Process of Induction, properly so called, or the search, by immediate observation, into the Causal Connection and Laws of the Phenomena and Processes with which we have to do. An inquiry into the simple method of experiment and into the individual steps and means by which it may be facilitated .... . . 82

I. The observation of the phenomena in question under the greatest possible variety of circumstances and relations . . .92

II. Comparison of similar Phenomena, &c. with each other ; employment of Analogies . . . . . .97

III. Application of the Numerical Method, or Statistics . . 106

Section IV

Characteristics and Value of the Knowledge which may be acquired by the Observation of Natural Objects, and by immediate Deduction from them. Experience, Empirical Laws, and their Scientific Importance . . 116 xii CONTENTS.

Section V. Page

Of the Methods of Investigation and the auxiliary Processes through which alone we can attain to higher and more exact Scientific Knowledge. — Analysis and the Synthetical (Deductive) Method . . • 145

Progressive Resolution of many and complicated, into fewer and more

general, Laws. Process of Reduction or Generalization . . 145

Demonstration of the causal connection of individual phenomena and processes, and of the laws of operation of individual determining circumstances and influences. Deduction of the causal connection of the complicated processes and influences of medical science . . 152 Reduction of numerous apparently heterogeneous phenomenaand processes to one and the same essential process and causal connection. Resolution of numerous complex laws into simpler, or more general and higher laws . . . . .192

Section VI

On certain Auxiliary Operations and Processes. Observation and Experiment. — Hypotheses, Comparison or Analogies, and the Calculation of Probabilities in General — Technicology, Terminology and Definition, Description. — Grouping or Classification .... 222

I. Observation and Experiment .... 223

II. Hypotheses, Comparison or Analogies, and the General Calculation

of Probabilities ..... 266

III. Language, Terminology and Definition, Description . . 288

IV. Classification ...... 336

SECTION VII. On Fallacies, their different species, sources, and importance . 353

I. Errors in the whole Mode of Contemplation, or Conception and

Judgment ..... 375

II. Errors in the Discovery of the State of Things . . . 388

III. Errors in the Comparison and Deduction of General Principles especially in relation to the Causal Connection of certain Things . 399

C0NCI,USI0N

INTEODUCTION.

As I feel conscious that the title of my book may, with many readers, lay it open to a degree of doubt respecting its precise purport, I think it desirable to anticipate some of the questions which may naturally arise, by a few words in the way of introduction.

What, it may be asked, are we to understand by the term Medical Logic ? In what relation does logic stand to medicine and to natural science in general ; and in what degree is the study of it likely to promote and facilitate the peculiar objects such sciences have in view ? Will it assist our investigations into the structure of man ; or may we, by its aid, expect to arrive at a fuller comprehension of natural science in its various branches, and thus be enabled to advance more safely and practically ? Will it afford the physician means whereby to understand the condition of his patients more clearly, or endow him with more skill in the treatment of disease, or render him more successful in its prevention ? Such were among the questions which I put to myself and carefully considered, before I could resolve to proceed with this attempt.

As regards the title "Medical Logic," I might have found many others as fitting, or even more so; but none so

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short. It expresses at once the aim of this work ; which is to set forth the importance of a correct application of logic to medical facts and inquiries, and to show the advantages it may render to natural science in so far as logic is connected with such questions.

I need scarcely remark that we are not here dealing with the ordinary logic of the schools, which I must leave to professed logicians. In the promotion of the practical object which we have in view, the term " logic " is taken in its widest sense and considered as " the science which acquaints us with the processes by which the mind of man, whether working in direct or indirect channels, may arrive at that establishment of fact in the correct appreciation of nature which constitutes empirical truth."

For the natural philosopher or physician no more knows by intuition what he needs to understand and learn, than he does anything else throughout nature. He must owe his insight into all these subjects to observation and experiment ; or, in other words, to his experience and the inferences with which it supplies him. By his own efforts, and by many collateral means, he must endeavour to arrive at knowledge; for truth is the philosopher's stone which we all seek and are still, except in miserable fragments, so far from having found. Yet there are certain mental processes, by the aid of which we are able to investigate the actual occurrences in nature; and through these logic is our guide. It teaches us how, by observation, experiment, and inference, we may overcome the obstacles that stand in the way of a clear comprehension of whatever natural phenomena we have to do with, and thus brings us, by a careful induction of processes, to the knowledge not only of their causal connection with each other, but also of their governing conditions and laws. It further shows us to what extent observation and deduction must be carried, and what requirements they must fulfil, before we can rely upon them as upon acknowledged facts and truths; and explains to us the mode of demonstration by which an assertion or inference, whether drawn from our own particular province of inquiry, or from the wide field of general natural science, may be established as true and proven; and an individual experience be accepted as a permanent truth.

It will enlighten us in any given case, as to the degree of correctness with which an experiment or a fact has been observed and interpreted. It will thus enable us to judge whether the conclusions we are inclined to draw from it (our general abstractions of laws for the science, and of rules for the art), follow strictly in the track of experience : it will also teach us to what extent we are justified in relying on them as on thoroughly demonstrated experimental truths and facts. In short, if it be the object of logic to teach us to think and judge correctly; if it be in all cases the science of exact demonstration, holding up the test whereto to bring our judgment, assertions, and conclusions, then must it (if employed so as to promote our interests and those of natural philosophy in its widest signification,) assist us in finding that which is the especial object of our search. By teaching us to appreciate our discoveries, whether real or imaginary, at their exact value, it will enable us to employ them to the fullest advantage, whether in the more immediate service of science, as in elucidating its laws and principles, or in extending the practical application of them, e. g. to the rules of therapeutics. Logic, therefore, in this more special signification, has much to accomplish. It must also be confessed that we are now asking of it services which have not often been demanded of the logic of scholastic philosophy, and such as it has still less frequently rendered. The father of logic, the great Bacon, has complained that the latter is almost useless for discoveries in the sciences, and for the investigation of truth. Men, says a certain Frenchman, have often believed themselves to be profound whilst they were only hollow. However this may be, we here take logic and its objects only as they are to be understood in medicine and in natural science in general ; and we therefore give it an acceptation in which philosophers and professed logicians cannot alwaysemployit, because theyare often too little acquainted with all the details and peculiarities of the subjects and objects of investigation with which we are occupied, and, consequently, with our particular wants and difficulties.

Logic, in this sense of the term, is the appointed cultivator of a soil, more or less crude and barren, wherein it must sow with patience, and in due time it will reap, a sound and nutritious aliment. It then becomes, both to the physician and the naturalist, the science of sciences, the "ars artium," in the fullest sense.

Thus, when we speak of Medical Logic, we simply mean the application of the science in question to our own special province. "We only seek by its aid to explain and develop more clearly the ways and means, the various processes, by which the natural philosopher, the physiologist, and the physician are accustomed to proceed in their investigation of phenomena, occurrences, and influences. It is the province of Medical Logic to point out how we may best observe, investigate, and experimentally test all those processes, influences, and occurrences ; those causes, so to speak, and eff'ects, under whose influence man and all living things are born into the world and continue to exist. It must lead us to ascertain the conditions of the living body, and to observe through what peculiar changes it passes from health to disease, and from this again to recovery. This science must determine the exact point to which our observations and experiments ought to lead us ; it must limit the inferences which we' "draw from them in relation to causal connection, and will thus preserve us from building up rash, uncertain conclusions upon generalizations derived from a doubtful, or even erroneous experience, and conduct us, by an exact method of demonstration, to that accurate investigation of nature, which, allowing her to speak for herself, enlightens us as to the real state of things, and so becomes our guide in deducing, with the greatest attainable certainty, those rules by which we must abide in our technical progress as physicians.

It is not, indeed, from logic, but from the science, whatever that may be, with which he has to deal, that the natural philosopher or physician must gain the knowledge of the facts and principles he requires; its province is but to guide him in the correct application of them and to enable him to judge whether the processes which are at work, eitlier in his own mind, or in those of others, for the elimination of certain truths, attain to, or fall short of the desired aim. It leads him in the case of any branch of science, to discriminate between the certain, the doubtful, and the erroneous. For we may at all times and in all cases rely upon our investigations, abstractions, deductions, and generalizations, as correct and true, in proportion as they stand the test of an exact and comprehensive logic ; and should they fall short of its requirements, it will not fail to point out the path by which we may arrive at more certain knowledge and more genuine truth, by providing us with an infallible test to try and prove (whether in observation or deduction), both our own thoughts and those of other men, and by bringing us, through a careful avoidance of error, to a more perfect comprehension of truth.

But those phenomena and processes in the living body which, under the actioft of the manifold influences of external nature, have ever been the especial object of medical experience, have in their nature nothing isolated, or tending to separate them from the general field of philosophical inquiry. "What we are accustomed to call disease, is but a peculiar change or process in the living organism, under the action of some of those influences from without, which affect the maintenance, loss, and recovery of health ; and these changes are a part — a very small one — of the great whole of nature. A given living being can no more be regarded as perfectly normal and healthy than as perfectly the reverse ; the latter condition would evidently be equivalent to death. It may therefore easily be understood why we cannot here confine ourselves to those phenomena and processes which are the special province of the physician. A logic such as medicine is in want of will, in truth, be equally applicable to the whole wide field of natural science, and, indeed, to all the so-called experimental sciences ; its doctrines and rules being essentially the same, whether they serve the physician or the physiologist, the physicist, chemist, or geologist, in the investigation of his particular objects, phenomena, and processes. Its application to questions and objects in the medico-physiological department is, however, of special importance here.

After what has just been advanced with regard to the aim and province of logic, as we here understand the term, there can be little doubt of its value to medicine, as well as to natural history in general. Whether the problems which these ofl"er it can, in their whole compass, be solved by any one individual, and especially by the author of this work, is a matter of reasonable doubt ; not so the essential nature of the service which their solution, if once effected, would render alike to the individual investigator and to the study of natural history and of medicine, whether considered as a science or as an art. Our object here is simply to establish truths and facts, so as to employ them correctly for certain practical purposes.

And these services acquire a double importance in a study such as medicine, where one of the most valuable possessions of man, his health, is the mediate or immediate object of investigation and treatment ; and where, on the other hand, our comprehension and capability of action* have attained to less certainty and infallibility than in any other department; for even to the present day, it is acknowledged that there is scarcely any department of human knowledge, in which the number of established truths and facts, which no one doubts or attempts to shake, is so small ; in no other field are our rules of action so uncertain and disputed as in medicine, the noblest and most important of all arts.

The safest data which we possess are individual observations, or empirical propositions in reference to the surface of the living body, and to the occurrence and succession of certain phenomena and processes within it. Of their internal connection, on the other hand, and of the essential conditions of their existence, course, and cessation, we know, as yet, next to nothing. We have more or less admissible views and hypotheses concerning them, but no thoroughly understood and firmly established facts and laws — therefore, no system. And in medicine, as in all cases where personal views and interests uncertain and often arbitrary theories, are defended or attacked, we sometimes find a rashness, or even presumption in the hypotheses, and a bitterness between the disputants, such as do not obtain in departments where a scientifically established, and, consequently, calm insight, has taken the place of mere opinion and subjective, a, priori, conjecture.

Just as medicine and physiology have entered into closer connection with natural history in general, and with chemistry and physics in particular, so the methods of investigation and the whole process of demonstration in the latter have been more and more adopted in the former. Scientifically educated and thoughtful men now ask themselves other questions, and put their experience and scientific investigations to other'tests than they were of old accustomed to do. But through this the discontent of many has but reached a higher pitch. We have seen faith in medicine — as an active agent — shaken on many sides, and a disposition to doubt and question has gained the more ground in proportion as what has been offered has the less corresponded to the demands of the increased intelligence and wider views of the age. A more exact calculation has in so far lowered the standard of our supposed wealth that it has seemed to us to be brought down to poverty itself; and thus one man, in his first excitement, has discarded, perhaps, too much of his previous knowledge, and despaired, more than was reasonable, of the powers of the human mind ; while another has been oppressed in a still higher degree by the responsibility of his duties as a physician, and this through despairing, perhaps, more than was necessaiy, of his art.

But as one extreme generally calls forth and accompanies another, so has it also been with us. We have seen this scepticism and tendency to critical negation opposed by the greatest confidence, or even arrogance, often combined with the superstitions and mysticism of times long passed away. We have seen the circumspect and, perhaps, too timid physician, who endeavours to instil into his practice a truly scientific spirit, confronted with the boldest speculation, and with the most thoughtless and narrow empiricism : just as we see, in other departments, a boundless and injudicious admiration of, and adhesion to what is old, opposed, without discrimination, to all that is new.

It can scarcely be doubted, however, that the greater number of these disputes and errors have frequently arisen, less from the insurmountable diflSculties of our subject, than from the want of a better understanding of the actual state of things. We have to blame the deficient employment of the necessary methods of investigation, and to accuse ourselves, in treating so delicate a subject, of a neglect of the doctrines of sound logic. And we must remember, in order to judge of the fitness of the present attempt, that many as are the difficulties of our subject, it is less to these difficulties than to our own want of caution, that we are indebted for so many false steps and failures. Against these, a careful logic would arm us, by imparting a clearer insight into nature, and into the special requirements and difficulties of our subject, while it at the same time provides us with rules for the critical appreciation of all our experiences and our theories. It not only exacts scientific perception, but also teaches us, D. V,, more aud more to abhor exaggerations and aberrations, in whatever direction they may point ; and these will be the more carefully shunned, the more physicians and physiologists become imbued with, and elevated by its doctrines.

Many of my readers will perhaps think, that, after all, logic can but assist us to theorize somewhat better than before, or at most to clear up and facilitate our critical examination of the notions and views presented to it. Of what value, it may be urged, will be all the theorizing and speculation through which it would profess to guide us, when we come to practise at the bedside ? Who has not heard so-called practical men say that medicine is a purely empirical science ; that everything depends upon facts and correct experience ; or, perhaps, that the power to cure is the main point ? All arguments and theories, they say, do not enable the physician to treat his patients more correctly ; in an art like medicine they rather do harm, or, at best, no positive good. It is there we are in need of experience — facts, and above all, remedies and their correct employment : all the rest is evil.

Further on I hope to point out what, in medicine and natural science, is the true signification of theory ; and, while I establish a distinction between correct and incorrect speculation, to show how frequently these are confounded. But it is the very fact of this confusion which explains, and in some degree excuses, the mistrust of all theories and so-called systems, and brings contempt upon the idea of methodical progress in our science. It is unfortunate thut there is, perhaps, in no other department, more real ground for such dislike and mistrust than in ours, where all theories and systems have so far proved deficient, and at least, in some degree, erroneous ; and where the very nature of the subject induces a necessity of their appearing less certain in proportion to our success in making them more comprehensive, subtle, and profound. But these false theories, &c., have always returned to their nothingness, and often immediately upon their construction.

Yet the merely practical man, the so-called empiric, is none the less blameable in his feeling of repulsion and mistrust. Would he, who, on the basis of every insignificant fact, opposes mere experience to theory and speculation, seek to apply that which holds good of monsters and precocious births, to that which is brought forth after the usual manner? He who sees in theory and experience two antagonistic states or tendencies, only proves that he has by no means attained to a clear perception of the essential meaning of theory and reasoning. It may be sufficient here to state that the physician who seeks to understand the condition of his patient, and by the aid of such knowledge, to cure his disease, cannot, however earnestly he may endeavour to do so, accomplish this without theorizing. He who doubts this does not even know how impossible it is to reflect upon, i.e., to form for himself any notions of even the simplest vital phenomena and diseased conditions, of the mode of operation of a remedy, or of any other occurrence in nature, without having already theorized and speculated concerning it — more or less correctly according to circumstances. Even the savage cannot observe anything in nature around him, i.e., simply recognize it by his senses, without seeking to interpret and to form for himself some notion concerning it. Even he endeavours to determine its origin and the mode of its development; he assumes one thing as an effect, and another as its cause ; though, perhaps, in the end, only some god or demon who, as he imagines, produces and controls it.

Let us take the case of a patient suffering from inflammation of the lungs, — a disease of frequent occurrence, and comparatively easy to recognize. The physician does not see this disease, however, any more than he does any other. He infei-s its existence from a number of local or general phenomena ; and traces it through symptoms which he knows have been observed in essentially the same form, combination, and order in other persons suffering from the same disease, But yet he knows next to nothing of the conditions and causal connection — in short, of the exact nature of those phenomena or derangements which, taken collectively, he interprets as and designates "inflammation of the lungs." The most detailed and conscientious investigation of the physical, chemical, and objective, as well as subjective, symptoms in the chest, pulse.

temperature, blood, excretions, or sensations, &c., in the patient, does not give him the least information on this subject, any more than the post-mortem appearances. And yet, every one who feels any interest in his science will wish to learn, and will therefore reflect, why his patient has been attacked by this disease, and what is its peculiar nature ; what changes or derangements are essential or determining; and which of them, on the other hand, are dependent, comparatively subordinate, and accidental. But so soon as he thus reflects at all, and even the most strictly practical man cannot refrain altogether from doing so, he also theorizes, and that, for the moment, very much at random. He entertains, perhaps, certain views concerning the operation of frost, moisture, and what is termed " taking cold," upon the living organism ; and, on the other hand, concerning plethora and similar general predisposing circumstances in his patient. With all this he will soon endeavour to account in some way or other for the development of the disease. He will further form certain notions concerning the origin of the fever, of the buflSng of the blood, of its accumulation in the parenchyma of the lungs, and of their so-called hepatization, and of the relations these bear to the buffed, or otherwise altered blood, to fever, heat, and other analogous derangements or phenomena.