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 
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