April, 1917] Tumors in Dogs 179 



Group 1. Two tumors fall into this group. Each presents 

 a fairly definitely encapsulated nodule in a gland, both of whose 

 lobes are enlarged to about an equal extent. The one was from 

 an old male and the other from a rather old female in a late 

 stage of pregnancy. In the gross, each nodule is buried in the 

 substance of the gland, but its outline can be distinctly made 

 out on the surface before sectioning. Each nodule is surrounded 

 by dense fibrous tissue and composed of a soft and apparently 

 very cellular tissue. 



Microscopical examination reveals compressed, but fairly 

 normal thyroid tubules surrounding the nodule. The cells of 

 these tubules are cuboidal. The lumina are irregularly ovoid 

 in shape due to compression. The secretion is small in amount 

 and only faintly stained with eosin. Within a capsule of dense 

 connective tissue can be seen a mass of epithelial cells resting in 

 scant stroma. (Fig. 1). There are, however, a few trabeculae 

 running through the tumor and these have taken on a mucoid 

 appearance, a change which is frequently seen in the connective 

 tissue supporting the tumors of the thyroid. Among the tumor 

 cells, every stage of transition can be seen from solid cords of 

 cells to tubules containing colloid and resembling closely those 

 of the normal gland. Mitotic figures are difficult to find. On 

 account of the greater lack of differentiation on the part of the 

 epithelium, the more extensive necrosis and the more definite 

 invasion of the capsule, the distinct impression is gained that 

 the second tumor is growing much more rapidly than the first. 

 It is of especial interest since pregnancy usually exerts an 

 inhibitory influence of neoplastic activity. In both specimens 

 the point of invasion of the capsule is adjacent to the cells, 

 showing the greatest lack of differentiation. As was noted in 

 the second specimen a goodly portion of the center of the nodule 

 has undergone necrosis. At the margin of this necrotic area, 

 the cells have arranged themselves concentrically around blood 

 vessels. The intervening tissue is necrotic, so that a peri- 

 theliomatous appearance is given to the tumor at these points. 

 In the second specimen, also, tumor cells are observed growing 

 in the lymph spaces. No metastasis is demonstrable in either 

 instance. 



The enlargement in these glands is due to a definite cancer 

 not unlike the so-called proliferating struma seen in the thyroid 

 gland of man. Apparently, also, here as in man, the tumor 



