_^^2 BULLETIN OF THE BUREAU OF FISHERIES. 



strate clearly in a few generations the exact importance of blood relationship to sus- 

 ceptibility and immunity. To guard against possible accidents obviously a series of 

 such experiments should be carried on at the same time and to this purpose it would 

 be necessary to devote the entire activities of a fish-cultural station for a period of years. 



The importance of such an investigation to the question of immunity in goiter 

 and cancer would certainly justify such an undertaking, aside from the possibility of 

 practical results to fish culture. Only in this way can the importance of inbreed- 

 ing as practiced in fish culture in the production of a general susceptibility among 

 domesticated fish to this disease be properly determined. It is a common assumption 

 that hatchery fish are more or less inbred. We have emphasized this idea in our 

 earlier statements. A marked susceptibiUty of at least one lot of pure marine salmon 

 species, i. e., the humpback, and in fact the occasional occurrence of the disease in 

 wild fish, indicate that inbreeding as such, except by the perpetuation and accentua- 

 tion of such susceptibility, may not be considered an important factor and the facts 

 developed in connection with the rainbow and brown trout at Caledonia clearly show 

 that fish-cultural inbreeding may finally develop a markedly resistant strain. 



To what extent spontaneous recovery from the disease results in acquired immunity 

 is not easy to state. There are many facts in this investigation which indicate strongly 

 that recovered fish remain immune for a considerable period of time if not indefinitely. 

 An experiment to determine definitely this question, although carried out with too 

 few individuals, failed to realize the development of visible tumors in recovered fish 

 at the end of one year, although placed in one of the lowermost ponds where the inci- 

 dence of the disease continued to be high. 



McCarrison (1906), in his study of endemic goiter in the Chitral and Gilgit Valle^^s, 

 gives striking examples of family predisposition to goiter and refers to the frequent 

 occurrence of goiter in nursing children where the mother has the disease. Schittenhelm 

 and Weichardt (191 2), in their recent monograph on endemic goiter in Bavaria, state 

 that it is easy to trace family predisposition to goiter and append family trees of some 

 13 families, from which it may be readily seen that certain families show a remarkable 

 incidence of the disease, which is especially marked in children where one or both parents, 

 and especially when both parents and grandparents, are affected by goiter. There 

 are several experimental studies in the lower animals indicating family susceptibility 

 to cancer, the most striking being the breeding experiments of Dr. Maud Slye (1913"), 

 and recent statistics emphasize the well-known fact of family predisposition to cancer 

 in human beings. Racial immunity to cancer has been shown by Levin (1910) to be 

 very marked in the American Indians. This fact appUes to isolated tribes of Indians 

 living upon reservations extending from the northern to the southern Hmits of the 

 United States, where the Indians for a period of 20 years have shown almost complete 

 immunity to cancer, whereas the whites living in the immediate neighborhood show 

 the usual incidence of cancer characteristic of the white inhabitants of the country. 

 That such immunity is a special immunity to cancer and not a general resistance to 

 disease is indicated by the fact that the same tribes of Indians show an unusually high 

 mortality from tuberculosis. 



