384 Fortieth Annual Meeting 



question is how much of the thyroid enlargement is cancer 

 or where is the dividing hne, rather than whether or not 

 the process is cancer. Cancer is preeminently a subject for 

 the medical specialists and it is to these we must look for 

 the diagnosis of the nature of the lesion. That this thyroid 

 tumor in fishes includes in its various stages of development 

 both goiter and cancer is the practically unanimous verdict 

 of the cancer authorities and is denied by none. Every 

 visible tumor in the thyroid region is not necessarily a 

 cancer, however. From the standpoint of fish culture we 

 need not attempt a separation of our affected fish into the 

 goitrous and cancerous, but we must recognize in practically 

 all domesticated salmonoids an underlying goitrous condi- 

 tion out of which cancer may at any time develop. Just 

 when and where this cancerous stage begins is beyond any 

 sharp definition, but when fully established it is as well 

 recognized microscopically as the earlier goiter. If one con- 

 siders the large number of fish with enlarged thyroids it is 

 doubtless true that cancer is comparatively rare among 

 them, for most of them are in the early stage of goiter. 

 The enlargement is arrested in most individuals and does 

 not even become visible externally. In many it remains 

 small or scarcely visible. In the few others it proceeds to 

 relatively enormous size with usually the development in 

 various degrees of the cancerous character as evidenced by 

 its structure and tendency to infiltrate or invade other 

 tissues. It is, of course, true that the appearance under 

 the microscope, while the chief historical criterion of cancer, 

 is not the only or controlling one. Transplantability into 

 other individuals and the occurrence of metastases or de- 

 posits carried from the original growth to distant organs 

 through the circulatory systems have been held to be in- 

 herent properties of the cancer process, and where they 

 occur all doubt of the cancerous process is removed. These 

 characters are not always exhibited, however, but to prove 

 their absence would require a mass of negative results from 

 prolonged experiments which if obtained at all will not be 



