Pusch: Inbreeding Live Stock 



89 



sheep as follows: The first four close 

 matings gave seven lambs of good con- 

 formation and development. Cross 

 breeding, on the other hand, gave two 

 lambs which did not develop well. 



Summary. — Inbreeding creates homo- 

 zygous germ plasm, producing animals 

 that breed true, and tends to produce 

 uniformity in the breed. Deliberate 

 and moderate inbreeding has proved 

 itself necessary and useful in live stock 

 improvement, and the reproductive 

 capacity has been favorably influenced 

 thereby. 



GENETICALLY SUPERIOR STOCK 

 NECESSARY 



Success in inbreeding is only pos- 

 sible where breeding stock has a strong 

 constitution and perfect health. It is 

 not successful in breeds that are too 

 highly refined, and the feeding and 

 shelter must be given careful attention. 

 According to Pusch, if the above condi- 

 tions are not fulfilled, the offspring from 



close matings may be over-refined in 

 skeleton, giving small yields of milk, 

 lacking in vitality, and showing low 

 fertility. Existing defects make in- 

 breeding especially dangerous . The cer- 

 tainty of inheritance applies to the 

 defects as well as the strong points of 

 the animals. Inbreeding, therefore, 

 requires continued and careful study of 

 the herd. 



Very close inbreeding should be rec- 

 ommended only when special con- 

 siderations justify and when the breeder 

 is fully conscious of the possible out- 

 come. There is an increasing tendency 

 to discourage such a method in Ger- 

 many. Moderate inbreeding and line 

 breeding have been used to good advan- 

 tage in Germany. Carelessness in ma- 

 tings and improper maintenance of the 

 animals have greatly increased the 

 dangers from inbreeding. Inbreeding 

 as a practice can only be carried on 

 profitably where all undesirable traits 

 have been avoided in the breeding stock. 



Heredity of Cancer 



It is, of course, only in accord with 

 common observation that tumors may 

 develop into sarcomata or other malig- 

 nant types of growth. The fact that 

 multiple fibroneuromata ,do so bears on 

 the question of "heredity of cancer," 

 which is so much discussed. 



This question is a perennial one. Of 

 late it has come to the fore because of 

 the doubt cast upon heredity of cancer 

 by life insurance actuaries and statis- 

 ticians using the method of mass sta- 

 tistics. On the other hand, new evi- 

 dence for the inheritance of cancer has 

 come from the experimental patholo- 

 gists whO' all agree that in mice there 

 are strains that cannot grow cancers 

 and others in which they grow rapidly. 

 The hereditary behavior of such strains 

 has even been investigated experiment- 

 ally by Tyzzer and Little. Now the 

 cancers of mice are so entirely like 

 those of man that it is extremely prob- 

 able that if the one has an hereditary 

 basis the other has also. 



Another reason for the view that cm- 

 cer is hereditary is that there are rTc^s 

 of men who are almost immune to can- 



cers, such as the American Indian, full- 

 blooded negroes and some aborigines of 

 Australia and the Pacific Islands. Also, 

 there are racial peculiarities in the or- 

 gans affected by cancer ; among the 

 Japanase women cancer of the genera- 

 tive organs is about as common as in 

 Great Britain, but cancer of the breast 

 only one-tenth as common. Also, we 

 cannot overlook the significance of such 

 facts as that of the occurrence of sar- 

 coma of the eyeball in three genera- 

 tions in the direct line and four in- 

 dividuals of the middle generation of 

 this family (Silcox, 1892). 



Finally, the fact of cancer villages, 

 where there has been much intermar- 

 riage, is strong additional evidence of 

 the racial significance of liability to can- 

 cer. In view of all these considerations 

 we must consider the presence of an in- 

 heritable factor in cancer as practically 

 certain. But we are, neverthelss, very 

 far from a knowledge of the law of its 

 inheritableness. That is a matter for 

 future investigation. — Eugenics Record 

 Office Bulletin, No. 19, October. 1918. 



