DISEASE AND RELATED PHENOMENA IN ANIMAL BREEDING 527 



defectives occur from generation to generation in domestic animals, 

 they are immediately condemned so far as breeding purposes are con- 

 cerned. Little, therefore, is known concerning the inheritance of defects 

 in animals except in rare cases where the defect may be of some use to 

 man. We refer particularly to such characters as the polled condition 

 in cattle, hornlessness in sheep, mule-foot in hogs, taillessness in cats, 

 and like characters. Among them we might also include the famous 

 Ancon sheep, now extinct. A case of an extremely malformed, defective 

 condition is that reported by J. Wilson in Dexter-Kerry cattle. These 

 cattle occasionally produce calves which are monstrous and live only a 

 few hours, but they all conform to a definite type. Wilson describes 

 them thus. "The body is short and stout; the upper jaw is short, giving 

 the head a bulldog appearance; the legs are extremely short, being little 

 more than a finger-length ; the tail arises from well up the back ; and the 

 ventral skin is unclosed so that the intestines protrude." Apparently 

 in this monstrosity we have a simple factor difference from the normal 

 form of such a nature as to lead to total incapacity for independent 

 existence. This condition is almost certainly the outcome of matings 

 of normal individuals heterozygous for a defective recessive factor. 

 The only moral that need be pointed out here is that a surprisingly large 

 proportion of defective conditions are heritable. The animal breeder 

 is, therefore, fully justified in avoiding so far as lies within his power 

 breeding from defectives or even from normal individuals belonging to 

 defective stocks. 



Immunity to Disease. Animals may exhibit different sorts of im- 

 munity to disease. Thus there is a certain kind of racial immunity 

 which is just as characteristic of a given race as its morphological charac- 

 ters are. Fowl cholera and foot-and-mouth disease do not affect men. 

 Apparently the degree of relationship may be even much closer. Thus 

 according to Tyzzer susceptibility to transplantable tumors varies in 

 different strains of mice. Two strains of common mice, one from Buffalo, 

 N. Y., and the other from Providence, R. I., and a strain of Japanese 

 waltzing mice were used in the experiments. Although the investigations 

 were not carried on extensively enough to be conclusive, they do indi- 

 cate very definitely different degrees of susceptibility to various kinds of 

 tumors. It was found that the Ehrlich tumor developed in 30 per cent, 

 of the Providence mice and in 60 per cent, of the Buffalo mice. It became 

 established in the Japanese mice, but practically failed to develop. The 

 Jensen tumor developed in 40 per cent, of the Providence mice, but failed 

 to develop at all in the Buffalo and Japanese mice. A Japanese type of 

 tumor developed in all but three out of 145 Japanese individuals which 

 were inoculated, but failed to develop at all in common mice. In the 

 zebu we appear to have an analagous condition, for according to Pucci 



