The progress of pathology hitherto has been exactly parallel with the progress of philosophy itself, system succeeding system in genetic order. No other department of biological science has shown itself so little able to shake off the philosophical character, or to run in the career of positivism or pure phenomenalism. This unique position of pathology among the natural sciences is doubtless owing to the fact that it is a theory of practice, a body of truth and guess-work existing for the benefit of a working profession which is daily brought face to face with emergencies and is constantly reminded of the need of a reasoned rule of conduct. It is idle to attribute the philosophizing habit in medicine, or the habit of system-making, to an unscientific method in past times. The extremely various points of view from which the problems of diseased life are approached in the very latest and most authoritative writings are an evidence that the difficulty is really inherent in the subject-matter.

The positive progress of the biological sciences does not essentially depend on the philosophical conception of life as action and reaction; but the notion of action and reaction comes to the front in every page of a pathological treatise, and at every step of practice. In considering the forms of diseased life, if not in the study of living things themselves, we. are constantly driven back to that ultimate analysis. The influences from without, which make up aetiology or the doctrine of causes of disease, assume a position in medicine the urgency or immediate interest of which far exceeds that of the biological problem, “the correspondence between life and its circumstances.” The standing difficulty in pathology has been its relation to aetiology, or the relation of the ens morbi to the agens morbi. One of the most singular ways of meeting the difficulty is that of Paracelsus, who boldly perpetrated the paradox: “Ens ist ein Ursprung, welches Gewalt hat, den Leib zu regiren.” The five classes of entia of Paracelsus are a composite catalogue, of which (l)j (2), and (5) stand for influences from without, and (3) and (4) for spontaneities, dispositions, or liabilities within. From time to time the centre of interest has been shifted to within the body, as in the “animism” of Stahl, in the “vitalism” of the school of Montpellier (end of 18th century), and in the “cellular pathology” of Virchow. A discussion of the inherent difficulty of holding the balance fair between that which is “exopathic” in disease and that which is “endopathic” may be read in Virchow’s article, “Krankheitswesen und Krankheitsursachen,” written in reply to objections that the cellular pathology was inadequate. “What I wished to treat of in the Cellular Pathology,” he says, “was the behaviour of the elements of the living body in the usual kinds of illness, or, to put it more briefly, the history of the elementary processes of disease. Upon that basis, it seemed to me, the doctrine of the nature of disease should be built. The respective causes I adverted to only now and then; thus I spoke of poisons, and even fungi had a place in the cellular pathology, although a very modest one. If the Cellular Pathology had ever pretended to be a general pathology it would have contained also the whole of aetiology.” Thus far Professor Virchow writing in 1880. If we now turn to a text-book of the same date, which does bear the title of General Pathology, that of Professor Cohnheim, we find pathology defined as “an explanatory science which seeks (1) to discover the causes of disease, and (2) to ascertain the esoteric connexion subsisting among disease-manifestations.” It is only (2) that forms the subject of Professor Cohnheim’s two volumes; aetiology, he remarks, is absolutely without limits. It “comes into relation with” cosmical physics, meteorology, geology, sociology, chemistry, botany, and zoology; from these sciences it gets its subject-matter. In the general pathology of Cohnheim, accordingly, aetiology is omitted; and with it are omitted many of the problems underlying the philosophical systems of the past, which have “only an historical interest,” as well as much of the natural history of disease. General pathology, he says, knows no other direction and no other order than physiology, “and accordingly we shall take up successively, and in the same order as physiology would take them, the pathology of the circulation, digestion, respiration, tissue-nutrition, and the like” (the pathology of the nervous system is not included in the two volumes). Without adducing other instances of eclecticism in the contents of modern pathological text-books, it will be convenient to give a brief notice of the latest attempt at a philosophical scheme of diseases,—the Elemente der Pathologie of Rindfleisch, 1883.

There are certain groups of symptoms, says Rindfleisch, which recur with the uniformity of a type in the most various diseases, depending as they do upon one constant factor,—the human body and its structural and functional tendencies. The larger number of maladies do not arise autochthonously or “under a whole skin,” they are generated by certain morbific causes; and it is the variety of causes that corresponds to the variety of disease-species, or to those ever-changing sequences and coexistences of symptoms in which the experienced eye of the practitioner learns to distinguish one disease from another. The morbific cause is an invasion upon the normal course of our life, usually a strong and forcible interference with the physical and chemical constitution of a particular part of the body. The disease as a whole stands for the effects of this interference, and these effects flow in part from the nature of the morbific cause and in part from the nature of the body which suffers. That which is uniform in these effects flows from the nature of the sick body; that which is various flows from the variety of morbific causes. It is above all the seat of the disease, its duration, the sequence and combinations of the type-groups of symptoms which are determined by the morbific cause. Only this varying element can be used to distinguish one disease from another. Therefore there is only one truly natural principle of subdividing diseases and only one point of view in special pathology from which the construction of a natural system may be approached,—namely, the aetiological principle of classification and the aetiological system. In each group of diseases, and in each individual disease, the causation has to be inquired into as closely as possible and described after the natural-history manner; we have to ask how and where the cause acts upon the organism, and finally to show how, from this action and from the reaction of the organism towards the same, we may explain those special features of disease and that special morbid process which are peculiar to each group of maladies or to each malady individually. In a word, the species morbi are made by the morbific causes; all that separates one disease from another is contained in the cause; only the causal differences, and no other, furnish those units of disease-life which can be brought under genera and species.

If we now inquire into the categories of causation, according to Rindfleisch, we find that they are five in number, as were the categories of Paracelsus. They are (1) injury from without, (2) parasitism, (3) deficient rudiments and defective growth, (4) over-exertion, and (5) premature involution or obsolescence. It is impossible not to discover heterogeneous elements in this enumeration; it is a composite catalogue like that of Paracelsus, and we shall find it hard to say in the case of (3) and (5) whether we are dealing with the ens morbi or with the agens morbi.

A statement of the definition and scope of pathology similar to that of Rindfleisch had been given by John Simon in his Lectures on General Pathology. Diseases were for the most part the normal phenomena of life under abnormal circumstances. “When you know the whole case you are obliged to admit that, according to the normal constitution of the body, the symptoms in question ought to have followed the operation of those several causes.” The doctrine of disease, accordingly, is mostly an “exopathic” one, although a small residue of it may be “autopathic.” It is impossible, says Simon, absolutely to exclude autopathic diseased states; there may be some such, mostly developmental, which “are actual caprices and spontaneities of life, without any exterior causation whatsoever.”

The exopathic point of view may be said to be the dominant one at present; more particularly, it is from the aetiological side that the enormous aggregate of contagious and infective sickness is mostly studied. Thus in the nosology of Rindfleisch the whole of the specific fevers and infections (including even climatic fevers) are placed (tentatively) under the head of “Parasitism,” the parasites being minute living organisms having their independent place in the scale of being. The numerous researches of the parasitic school may be regarded as the most formal attempt as yet made to separate the study of the agens morbi from that of the ens morbi. 1

§ 2.— Introduction.

The plan of this article will be to take diseases as they occur in the concrete, and to apply an analytical method to them. In a given disease, or in an individual case of the same, the object would be to find the point of divergence from the beaten path of health, or, failing that, to seek out the nearest analogies in the physiological life for the unaccustomed and even grotesque things of disease. The effects of disease in man’s body may be likened, in a too pleasing figure, to the effects of a magician’s wand; there is

“nothing of him but is changed into something rich and strange.” This fascinating region of science is well outlined by Buckle in his remarks on the genius of Hunter :—

“In nature, nothing is really irregular or disorderly; if we are apt to fancy that the chain is broken, it is only because we cannot sec every link in it. . . . Being satisfied that everything which happens in the material world is so connected and bound up with its antecedents as to be the inevitable result of what had previously occurred, Hunter looked with a true philosophical eye at the strangest and most capricious shapes. To him they were neither strange nor capricious. They were deviations from the natural course; but it was a fundamental tenet of his philosophy that nature, even in the midst of her deviations, still retains her regularity.”

Hunter’s own words are: “Nature is always uniform in her operations, and, when she deviates, is still regular in her deviations. . . . It certainly may be laid down as one of the principles or laws of nature to deviate under certain circumstances.” The interest of this science, says Buckle, “depends simply on the fact that, when it is completed, it will explain the aberrations of the whole organic world.” The same science of deviations was provided for by Bacon in his classification of the sciences; and, after him, by D’Alembert, under the head of “Prodigies, or deviations from the usual course of nature,” in his classification for the Encyclopédie.

The science of deviations begins, in the writings of Hunter and of Paget, λvith the erratic forms of crystals, and with the indwelling power of crystals to repair injuries on the lines of their growth if they be placed in the proper mother-liquor. In the hands of each of these two pathologists this science next proceeds to elemental aberrations in the life of plants, where there is neither heart nor nervous system to complicate matters; and, so advancing from the simpler to the more complex, we should have a science of the abnormal coextensive with life itself. Without attempting to treat of pathology in that evolutional order, which proceeds from elemental pathology upwards, we may still adopt, for the narrower subject of human pathology, a somewhat analogous order, that is to say, a method based upon the facts of embryonic development. Confining our attention, then, to the processes of disease within the human body, and seeking out from among these the broadest of the facts, we shall find evidence, as we proceed, that the life of the body retains vividly the memories of its past. Nothing marks so generally the disease-incidents of life as crudity or recrudescence in the activities of cells, tissues, organs, and mechanisms. In other words, we shall find much in pathology to show that, when the organism goes wrong, it retreats to broader ground, or reverts to modes of life which it had come through. But, even in the normal functional and structural processes of the mature body, we find occasional evidences of the same reversion to embryonic modes of life. These are practically limited, in health, to the reproductive system, or to that part of life which goes to the maintenance of the species. Here we find periodicity still in full force, the same periodicity, primarily following the seasons, which underlies the life of plants and of most animals. The greatest example in the human body is the building up anew, from time to time, of an entire organ, the placenta, for the intra-uterine nourishment of the child; in this periodical formation we have a reversion, in the midst of mature life, to vessel-making and blood-making such as the body goes through otherwise only during its development. The provision for the nourishment of the child after it is born is a somewhat modified instance of the same kind. The full structure and function of the breast also develop periodically (although the framework is permanent), and each of these periodical developments is a repetition of the incidents in the original embryonic development of structure and function.

1 Literature. — Häser, Lehrbuch der Geschichte der Medicin und der epidemischen Krankheiten, 3d ed., 3 vols., Jena, 1875-82; Virchow, “Krankh ei ts wesen und Krankheitsursachen,” in Virchow's Archiv, vol. lxxix., 1880; Cohnheim, Vorlesungen über allgemeine Pathologie, 2 vols., Berlin, 1877-80; Rindfleisch, Die Elemente der Pathologie, ein natürlicher Grundriss der wissenschaftlichen Medicin, Leipsic, 1883; Siinon, Lectures on General Pathology, London, 1850.

It is when we come to the several tissues that we meet with the most striking reminders of persisting developmental characters, the most universal fact of the kind being the indwelling embryonic character of the common binding tissue. In that tissue, indeed, we have a constant reminder that in the midst of the very highest or most perfected modes of cellular life we are but a step removed from the most rudimentary. Thus in the brain and in the retina the elaborate nervous mechanism is supported on a framework of connective tissue; there is a morbid condition of these organs, called glioma, in which the connective tissue, or neuroglia, absolutely usurps the place of the nervous mechanism of which it is ordinarily the mechanical support; and this it may so completely do, as in disease of the pons Varolii, that even the outward form and markings of the part are not interfered with. An equally striking instance of a return to embryonic characters and predominance may sometimes be observed in the primitive nuclei of muscle; the muscle-fibres will be found to have surrendered their high function, to have retraced the steps of their development, and to have sunk their identity in a rudimentary form of cell-life.

Thus the body nowhere loses altogether the memory of the past, even when the periods of development and growth are, strictly speaking, ended. Among the normal processes of mature life there are such as amount to a recrudescence of structure and function; and an analogous recrudescence in the tissues is one of the most fundamental facts in the processes of disease. There are several advantages in proceeding in an exposition of pathological principles from this evolutional or developmental basis. It enables us to take up, in an order not unsuited to their importance, the sections relating to repair, to new growth of tumours, to errors of growth, such as rickets, to errors of blood-making, and the like. At the outset comes the process of repair, for which Paget has formulated the embryological principle as follows: “The powers for development from the embryo are identical with those exercised for the restoration from injuries; in other words, the powers are the same by which perfection is first achieved, and by which, when lost, it is recovered.”

§ 3.— The Process of Repair.

The spontaneity of certain polyps under injury is a good example of the indwelling power of all the cells and tissues to return to the established order, to the order and harmony which had been slowly acquired, and of which the memory is vividly retained. Trembley cut a hydra longitudinally, and “in an hour or less,” says Paget, “each half had rolled itself and seamed up its cut edges so as to be a perfect hydra. He split them into four; he quartered them; he cut them into as many pieces as he could; and nearly every piece became a perfect hydra. He slit one into seven pieces, leaving them all connected by the tail, and the hydra became seven-headed, and he saw all the heads eating at the same time. He cut off the seven heads and, hydra-like, they sprang forth again.” The recovery of perfection may be more gradual. Thus, Sir J. G. Dalyell (as quoted by the same writer) cut a specimen of Hydra tuba in halves; each half regained the perfect form, but only very slowly, and, as it were, by a gradual improvement of parts that were at first ill formed. In Tubularia indivisa, after the natural fall of its head, the stem was slit for a short distance down; an imperfect head was first produced, at right angles to the stem, from one portion of the cleft; “after its fall another and more nearly perfect one was regenerated, and, as it grew, improved yet more. A third appeared, and then a fourth, which was yet more nearly perfect, though the stem was thick and the tentacula imperfect. The cleft was almost healed, and now a fifth head was formed, quite perfect; and after it, as perfectly, a sixth and a seventh head. All these were produced in fifteen months.” This spontaneity resides in every living thing, and its efforts are directed by the memory of what the species had come through in reaching its place in the scale of organization; it is able, indeed, to make perfect reparation for injuries or losses only where the cells are little differentiated into tissues, or where the tissues are little specialized for diverse functions. In all animals, and most notably in the higher, this spontaneity is most effective for repair in the periods of development and growth. With reference to the degree of reparative power possessed, Paget formulates the rule as follows: “The amount of reparative power is in an inverse ratio to that of the development, or change of structure and mode of life, through which the anima! has passed in its attainment of perfection, or on its way thitherward.”

Healing by Granulations.— It will now be convenient to advance in medias res, and to give some account of the process of repair in man, where there is a breach of continuity in the course of the blood-carrying and lymph-carrying vessels, of the nerves, sinews, binding tissue, bone, fat, and skin. What is the effort that they each and all make to adapt themselves to the circumstances, in the case, let us say, of a stump after amputation? (The repair between the two ends of a broken bone will be discussed separately.) Disregarding the cases where the most perfect coaptation of parts is secured by...