362 PATHOLOGY ciple 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 aitiolo- gical 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 re action 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 dis ease 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 rudi ments and defective growth, (4) over-exertion, and (5) pre mature 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. Simon s A statement of the definition and scope of pathology simi- view. } ar to na t O f Rinflfleisch 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 doc trine 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 develop mental, which " are actual caprices and spontaneities of life, without any exterior causation whatsoever." Exo- The exopathic point of view may be said to be the dominant one at present; more particularly, it is from ^ ie ^tiological side that the enormous aggregate of con tagious 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 1 Literature. Hiiser, Lehrbuch der Geschichte der Medicin und der epidemischen Krankheiten, 3d ed., 3 vols., Jena, 1875-82 ; Virchow, " Krankheitswesen und Krankheitsursachen," in Virchow s Archiv, vol. Ixxix., 1880 ; Cohnheirn, Vorlesungen iiber allgemeine Patho logic, 2 vols., Berlin, 1877-80 ; Rindfleisch, Die Eleinente der Putho- li fjie, ein naturlicher Grundriss der wissenschaftlichen Medicin, Leipsic, 1883; Simon, Lectures on General Pathology, London, 1850. view " 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 see 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 pre viously 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 com pleted, it will explain the aberrations of the Avhole 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 classifi cation for the Encyclopedic. The science of deviations begins, in the writings of Hunter and of Paget, with 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 pro per mother-liquor. In the hands of each of these two pathologists this science next proceeds to elemental aber rations in the life of plants, where there is neither heart nor nervous system to complicate matters; and, so advanc ing 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 evolu tional 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 develop ment. 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 evi dence, 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 re crudescence 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 embryo nic 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, prim arily 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 nourish ment 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 nourish ment of the child after it is born is a somewhat modi fied 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 period ical developments is a repetition of the incidents in the original embryonic development of structure and function.
