These formations are in general alike rare in the veins and the arteries (see p. 207), although cancerous disease of the veins presents an exception to this rule.

1. A fibroid tissue occurs as an inflammatory product in thickening and sclerosis of the cellular coat of the vein. It is in a great measure the cause of the resemblance to the character of an artery exhibited by the diseased veins.

2. An anomalous osseous substance, - the so-called ossification of the veins. - It may be distinguished in accordance with its seat into a peripheral and a central form. It also varies in the character of its substratum.

a. The peripheral includes the process of ossification that takes place in an excessive formation of the lining membrane of a vein. It appears, as in ossifications of the arteries, in the form of plates, which, however, for obvious reasons, never attain the thickness of those which occur in the arteries. Its seat is in the venous wall. It is uncommon, and, except in extremely rare cases, very limited in extent. It commonly affects varicose veins, especially the saphena, and we occasionally observe it in the deep veins of the extremities, when they are in contact with ossified arteries, as, for instance, in the internal spermatic vein in males, or in the trunk of the portal vein or its splenic branch (of which we have examples in our museum); they must be ranked amongst the very rarest phenomena.

b. Central ossification includes two forms of concretions, differing in their substrata, namely, phlebolites and the ossification of the coagulum closing an inflamed vein (see Phlebitis) after its temporary metamorphosis into a fibroid string. Both lie in the canal of the vessel, either freely, or coalescing in the modes that have been already described, with the wall of the vein.

3. Tuberculosis does not occur either in or on the bloodvessels, as we have expressly remarked in our observations on the endocardium and the arteries.

4. Cancer is, on the other hand, by no means a rare phenomenon in the veins. There are two different ways in which it may occur: a. The walls of a vein are very often perforated by an adjacent cancerous growth, that is to say, the cancer attacks the tissue of the vein, like other tissues, and penetrates into the canal of the vessel. In this way, large veins, as, for instance, the trunk of the ascending vena cava, not unfrequently become entirely closed by exuberant cancerous growths lying on the lumbar portion of the vertebral column; and the same occurs in the veins of a cancerous organ, as, for instance, the renal veins, the portal vein, the hepatic veins, etc.

b. There is another form which is rarer, but of much greater interest, which may be termed primary cancer, to distinguish it from the former. It occurs in a vein, generally one of the larger ones, as a broad or narrow, pedicled, roundish, pear-like, single or lobular adventitious mass, or as a cylindrical mass adhering to the whole or greater portion of the circumference, and closing the vein. It sometimes is attached only loosely to the lining membrane by means of a gelatinous blastema, or its parenchyma penetrates into the tissue of the venous wall to various depths. According to circumstances, of which the most important is the duration of the existence of the adventitious product, it presents the appearance either of a fibrinous coagulum, or of an aggregation of primary cells in various stages of development, the whole mass commonly presenting the characters of medullary cancer. This form of cancer never occurs except in association with a large exuberant cancerous growth in some other organ, or when there is a widely diffused and rapid formation of cancerous tumors in many organs, especially of intense medullary cancer (encephaloid). It scarcely ever occurs in the organism, except as a secondary formation. The lymphatics in the vicinity of the original adventitious structure are very often plugged up and closed by the medullary cancer.

This cancer of the veins doubtless occurs through the absorption of cancerous matter by the lymphatics and veins into the mass of the blood; and, independently of the latter, it may be of spontaneous origin, and may be the result and expression of the highest degree of endogenous disease of the fibrin: the circumstances under which this disease has been observed accord with both these modes of origin.

Moreover, we must here include the coagulum which closes the veins and originates from the absorption of cancerous or ichorous matter - the phlebitis arising from cancer.