76 Op. cit., 51.
77 Virchow's Archiv, 1883, xci. 129.
The milk from cows thus diseased has likewise been regarded with suspicion, and the frequency of intestinal tuberculosis among children has been attributed to this source. Although the theoretical possibility of the escape of the bacilli into the milk of cows affected with pearly distemper is obvious, their presence in such milk is first to be demonstrated under conditions which necessitate their origin from the animal. If boiling the infective material for three minutes destroys its virulence, as claimed by Aufrecht, a ready means is offered of destroying the tubercle bacilli which may be present, not only in the milk from animals affected with pearly distemper, but in all milk which has been exposed for a certain time to an atmosphere which may contain the bacilli of tuberculosis. In the light of our present knowledge extreme hygienic precautions are only demanded in those cases where such a congenital or acquired basis (constitution) is present as facilitates the development of tuberculosis.
Morbid Growths.
In a system of practical medicine it is obviously important to include under the head of Morbid Growths not only what is spoken of by the surgeon as a tumor, but also those new formations of tissue which, in virtue of their nature, seat, manner of growth, and retrograde changes, produce an important series of disturbances in the physiological processes of the individual. The surgeon deals essentially with the swelling, which, producing irregularities in the outline of the accessible surfaces of the body, is regarded as an excrescence or outgrowth. It is important for him to realize the nature of this swelling, that he may follow a different treatment for the abscess, the wen, the watery accumulation, or the fleshy mass. The last is the tumor in the limited sense; it is the growth which, though called morbid, becomes so only in consequence of its presence being associated with symptoms whose existence and persistence interfere with the well-being of the possessor.
The physician, on the contrary, is more concerned with the tumor as a growth than as a swelling. The latter element in deeply-seated portions of the body may not be brought to his attention. The growth takes place in such a manner as to be productive of certain symptoms more or less serious, among which swelling is least obvious. The morbid growth to him becomes prominent as it displaces or replaces normal tissues by those newly formed, which may or may not be normal to the part in which the growth is situated. His tumor is therefore a morbid growth, a new formation, a neoplasm or pseudoplasm, rather than a swelling, a bunch, or an excrescence.
In a consideration of the general pathology of morbid growths the first question which suggests itself relates to the method of origin of the tumor. The tendency of the present seeks for a local cause, and the most recent theory, that of Cohnheim, demands an accumulation of dormant embryonal cells as such a cause. Cohnheim supports this view by the experiments of Zahn and Leopold, which show that foetal cartilage transplanted into the tissues of a mature animal may grow so rapidly as to present the characteristics of a cartilaginous tumor, while tissues transferred from the animal after birth do not increase in size, but are usually absorbed.
As the active elements of the growth are cells, and all cells admissibly arise from pre-existing cells, it follows that the primitive cells of a tumor are derived from those resulting from the segmentation of the ovum or are introduced from without. Numerous experiments have been made with a view to the inoculation of tumors, the transplantation of living fragments of the latter to the living tissues of a healthy individual, for the sake of producing a tumor, but hitherto almost invariably without success. The alternative remains that the embryonal cells are those whose derivatives are present in, and form the essential element of, the morbid growth. All tumors may thus be said to have an embryonal origin. As the segmentation of the ovum eventually results in the production of normal tissues and groups of tissues whose structure and function are wholly different, so the possibility of the production of abnormal groupings of tissue with corresponding irregular manifestations of function is obvious.
The cells of the part from which a tumor arises may be regarded as indifferent, those whose limitations of growth, like the early embryonal cells, are only determined by the changes they undergo, or their limits of growth may be already defined in kind, and their like be produced in the formation of the tumor. The origin of a tumor thus presupposes the existence of such indifferent cells, or the presence of those whose limit of transformation has already been reached. The leucocytes of the body, whether found as white blood-corpuscles or lymph-corpuscles, or as the wandering cells of connective tissue, are, as Virchow has indicated, such indifferent cells. Always present and apparently transitory, what they are to become can only be determined from their condition and surroundings at the time of observation. Although their actual transformation into the various cells of a more permanent type is merely a matter of inference in the growth of tumors, the evidence presented by Ziegler78 leads directly to the conclusion that their presence is necessary to the new formation of tissues whose growth is the result of an inflammatory process. These tissues may occur under such restrictions as permit them to be classified as tumors, and the granulomata, or tumors whose tissue resembles that of the granulations upon the surface of a wound, represent a well defined group in structure as well as method of origin.
78 Op. cit., 150.