402 PATHOLOGY between the two extreme positions it should be remembered that there -is nothing morphologically distinctive in these organisms found in diseased or injured tissues, that their so-called physio logical activity in disease is merely begging the question, and that their mechanical presence, even if they were always present in sufficient numbers, has not yet been brought into any intelligible relation with the symptoms and the morbid anatomy. On the other hand, there cannot be the slightest doubt that one of the greatest desiderata of surgical practice is to keep them out of wounds (see SURGERY). Tumour- Tumour-infection. This subject has already been treated of in infection, the section on "cancer," but it will be convenient to add a few re marks on the parallelism between tumour-infection and purulent infection. In both cases we have a primary seat of morbid action and a secondary infection, and in each case the seats of secondary infection correspond on the whole closely. The closest correspond ence is perhaps with sarcomatous tumours, which have the same relation to veins that primary infective inflammations have, and the same predilection for the lungs. Again, where the liver becomes the seat of secondary tumours, the first steps of the process of infection are on the whole parallel with those that may be observed in multiple abscesses of that organ, that is to say, the liver-tissues at a number of points undergo changes which are practically simul taneous within a certain radius, leading to a circumscribed abscess in the one case and to a circumscribed tumour -nodule in the other. Both the abscess-area and the tumour-area may be found at half-way stages of their development, the former being often recognizable in the section of a pyremic liver as a somewhat livid circular spot. In the tumour-process the morphological characters are always very definite, and the exciting agent has plainly come from the primary disease, carrying the structural marks of the pri mary disease in it. The primary inflammatory process wants the definite structural characters of the primary tumour-process, and still more does it want the endless variety of the latter ; but it is still a textural process of the body, and its secondary processes are like it. The tumour-analogy, therefore, is strongly in favour of the idea that purulent infection, and inflammatory infection in general, has an autochthonous origin in the life of the cells and tissues. Melan- Melanosis. The term "melanosis" is used in pathology in at least otic in- two distinct senses. It is applied, in the first place, to the general- fection. ization or secondary extension of a primary tumour (usually sar comatous), containing black or brown pigment ; and, in the second place, it has reference to a remarkable generalization or widespread deposition of black pigment in the bone-marrow and elsewhere in the horse, particularly in those horses which are apt to lose what ever hair-pigment they may have had. Each of these two very dif ferent cases has its interest for general pathology. The generalization of a melanotic tumour, even a very small one, is one of the most remarkable facts of infection. It is not unfre- quently seen in the case of the spindle-celled sarcomatous tumours which grow from the pigmented connective -tissue cells of the choroid tunic of the eye (not the choroidal epithelium of the retina). In such cases the primary tumour is serious enough from its pressure effects, but it is infinitely more serious from its infect- iveness. The liver may be full of large tumour -masses, black throughout or in part, and there may be other secondary growths elsewhere. Even more striking is the generalization which is apt to ensue from a subcutaneous melanotic sarcoma, or from a small spot of pigmented new growth on the basis of an old pigmentary mole, or noevus, or mother-mark (melanotic alveolar sarcoma). The secondary tumours occur at other points under the skin, often widely remote from the primary, and in the axilla, in the membranes of the spinal cord, in the liver, in the lungs, and even on the serous membranes. We have here to do with the ordinary considerations of tumour -infection, as already spoken of; but the presence of pigment in. the cells and partitions of the new growth raises a further consideration. If we collect all the secondary tumours from a case where infection has been extensive, and express from them all the pigment, we should get a very considerable quantity, perhaps half a pint, of a thick black fluid not unlike printers ink. The source of all this pigment has been perhaps a small speck of melanotic tumour-tissue in the skin, or, to mention a particular case, in the granulation-like tumour-tissue in the bed of the thumb nail after an injury. How is it that from so small a source so much of this black substance has been produced ? The pigment is, of course, contained within the individual cells of the secondary tumours ; these cells are a mimicry of the primary tumour-elements, and, as they reproduce the form and size of these, so also they reproduce their pigment -granules. So stated, there is nothing remarkable in the quantity of black fluid that may be collected from a case of generalized melanotic sarcoma. The primary tumour impresses the type of its own life upon a number of distant centres of cellular activity, so that these grow to be tumours, their cells at the same time becoming each a laboratory for the manufacture of pigment, extracting it from the blood for their erratic purpose. The true suggestiveness of these events is really in the way of analogy for another class of infections. It is often said that, in an infection like smallpox, the virus must be an independent living organism, because it multiplies within the body during the evolution of the disease, the body which had received a most minute quantity of virus becoming in its turn a centre from which a thousandfold of the virus may issue. Hut, if a small speck of melanosis may yield half a pint of inky fluid by so impressing the cells of the body that they become so many laboratories of black pigment, then we can understand how, in smallpox, the cells of the skin at many points become laboratories in like manner, not indeed yielding black pigment, but supplying that which has to the primary contagion of a case of small pox the same relation that the generalized pigment of nielanosis has to the primary speck or nodule of pigmented spindle-celled or alveolar sarcoma. It is not necessary n priori to go so far afield as the ferment - action of living organisms for an analogy of this thousandfold multiplication ; there is an analogy nearer home in the marvellous metabolic capabilities of the body s own protoplasm. Melanosis of the Horse. It sometimes happens that we find, in Melan the carcase of an aged grey or white horse which had been originally osis oi brown or black or other shade of colour, that the marrow of all the horse. bones in its body is changed into a uniform black inky pulp or fluid, that the clusters of lymphatic glands are full of the same in a drier form, and that there are black patches on the more exposed parts of the mucous membranes. This remarkable malady is not found except in horses whose coat had lost its originally abundant hair-pigment. Trousseau and Leblanc, who investigated the facts on a large scale at the Paris horse-knackers , were of opinion that in every horse which had turned white, more particularly if it had been originally black or brown or roan, the inguinal lymphatic glands were full of black pigment ; and they concluded that the pigment there deposited was the equivalent of the colouring matter that the hair had lost, and that the blood being, as it were, overcharged with colouring matter, had deposited pigment in unusual places. It is difficult to suppose that the melanosis in these cases is a mere quantitative equivalent of the pigment lost from the hair. The pigment of melanosis is more probably a true metabolic pro duct of cells ; and it is significant that it is most abundant, in the horse, in the old seats of haemoglobin-formation, namely, the red bone-marrow. The bone-mamnv (with other tissues as well) takes on a pigment-making activity, coincidently with the blanch ing of the horse s coat, and vicariously thereto. The melanosis of the horse is a striking instance of a constitutional i/talad//, that is to say, it illustrates the very important pathological doctrine that an error in one part or function of the organism entails vital consequences elsewhere. 1 16. SPECIFIC INFECTIONS. Infective disease of one kind or another stands for a very large part of the total sickness and mortality of man kind. It is entitled, therefore, to a larger space in a nosological outline than a single section at the end of an article. Each infective disease has to be considered by itself, from the natural -history point of view, and the salient facts of its history, geography, and ethnology, and its other particular circumstances to be taken along with its morbid anatomy and clinical history. It will be necessary, for the present purpose, to adopt a much more restricted programme, and to indicate little more than the place of the specific infections in the general scheme of disease. Of diseases that have the property of infectiveness we have already dealt with cancers and other malignant tumours, and with the common infective inflammations. Reference has also been made to erysipelas, which is sometimes not merely infective as regards the individual body in which it arises, but a source of infection (or contagion) also for other bodies through conveyance of a virus. In the communicable class of infections we have to include so ordinary and simple a malady as a common cold, which is notoriously apt to go through a whole household, having been acquired in the usual way by some one member of it. The great historical epidemics of influenza which have overrun whole continents from time to time are held by some to be little else than colossal 1 See Virchow, Gesammelte Abhandl. cms clem Gebiete dcr wissensch. Med., Frankfort, 1856, Cellular - pathologic, chaps, x. and xi., and Krankliaften Geschwiilste, vol. i. chap. 3, and vol. ii. (" Melanosis ") ; Billroth, AUgemeine chirurgische Pathologic, 8th ed., Berlin, 1876 (Engl. transl., New Syd. Soc., 2 vols., 1877); R. Koch, Actiologie cler Wundinfections-Krankheiten, Leipsic, 1878 (Engl. transl., New Syd. Soc., 1880).
