258 



BIOLOGY OF THE LABORATORY MOUSE 



The first is by the direct transfer of new-born young, reported and exten- 

 sively studied by Bittner (13, 18, 19, 22-28, see also Chapter 9). This 

 method brought to light the entirely unexpected and very interesting fact 

 that the new born young from "high" breast tumor stocks, when transferred 

 to nursing females of a "low" breast tumor stock, develop into animals 

 which in later life show an incidence of breast tumors very similar to that of 

 their foster mother. To a considerable degree the converse is also true. 

 The incidence of breast tumors among mice of "low" tumor strains can be 

 materially increased if they are fostered by "high" tumor females (Table 7). 



Table 7 



The second method of testing the influence of foster mothers is by the 

 transfer of fertilized ova from the fallopian tubes of "high" breast tumor 

 mice to the uteri of pregnant "low " tumor females. This technique as used 

 by Fekete and Little has given rise to a considerable number of viable young 

 developed from transferred ova. These mice upon maturity have shown a 

 breast tumor incidence characteristic of the strain from which their foster 

 mother was derived. The exact quantitative relationship as regards breast 

 tumor incidence among the fostered and transferred mice obtained by the 

 two methods has not yet been determined. The possibility remains that the 

 intra-uterine influences may prove to be more extensive and stronger than 

 those of the milk alone. On the other hand no such difference may be 

 obtained. The matter is under investigation. 



