14 LOUIS A. DUHRING;
nuclei of a morbid growth, the transferrence of these bo(iies to the blood, and the deposit of the wandering new-growth elements in the tissue or capillary net of a distant organ where the development and new formation of a tumor, resembling the original, takes place ; or the new-growth elements enter directly the blood-vessels, usually a vein, and are carried with the blood-current to a distant point ; in the latter case the name of metastasis by embolism is given to the process. The point of selection for the develoi)ment of the meta- static knot depends largely on mechanical grounds ; the embolic mass is carried onwards until it reaches a vessel (usually a capillary, for these masses are, of course, very minute) whose calibre does not allow of its passage; here it rests and develops. The histogenetic relations of tissues influence also the selection of the point of de- velopment. Mammary gland tumors are developed by metastasis, in the liver, partly because, the two organs are histogenetically related, both being glandular epithelial organs, partly also because the blood-vessel capillary net of the liver is quite the finest in the body. Sarcomata of the bones, being histogenetically related to other bones, have their metastatic knots appearing in bone at distant parts ; but not invariably, because the wandering elements of these tumors are in large masses and abundant, and, consequently, are liable to be strained out, so to speak, by any narrow-calibred capil- lary net through which they pass and develop in tissues not related to bones histologically.
Concerning the lesion of the parotid gland, the explanation is not so clear and definite as in respect to the bladder. It is possible to suppose that the invasion of this organ was a fortuitous occurrence resulting from the involvement of the surrounding parts and of the skin overlying it. It is well also to remember in this connection that the parotid gland is an epithelial structure, and that its tubules are to be included in the list of " epithelial surfaces." Whatever may be the explanation of its involvement, it is clear that it is not an instance of metastasis.
It may be well to mention that the enlargement of the lymphatics did not uniformly occur in glands seated near large lesions (for example, the axillary glands), and that the microscopic picture pre- sented by them was that of a hyperplasia. It was not the picture seen in glands situated near malignant growths, but rather that accompanying inflammation or a similar irritation.
In conclusion, attention must be fixed on the fact that the appearances, both microscopical and clinical, indicated the disease to be one produced by an infiltration of the tissue; the relations of the corpuscular elements to the tissue in which they are placed are the same as those found in other diseases in which an infiltration is unquestioned; the rapid rise and fall of the tumors, so called, show the nature of the disease to be of this character. No one ever saw a malignant growth, not even a sarcoma, rise in a night and disappear by the end of a week. The size and the structure of its cells does not throw one morbid growth into one class, and another morbid growth
