72 



Scientific Proceedings (89). 



have described to occur when animals are kept on a diet deficient 

 in the fat-soluble vitamine. The details will be published in the 

 Journal of Biological Chemistry. 



152 (1330) 



The effect of continued inbreeding on the tumor rate in mice. 



By Leo Loeb and A. E. C. Lathrop. 



[From the Department of Comparative Pathology of Washington 

 University Medical School, St. Louis, Mo.] 



In former investigations 1 we found that different strains of 

 mice differ very much in their tumor rate and tumor age; and that 

 these differences in tumor rate and tumor age were maintained 

 and hereditarily transmitted to the following generations through- 

 out the period of observation, notwithstanding the similarity of 

 external conditions under which the animals were kept. 



It was of interest to inquire how continued inbreeding of these 

 various strains would affect the tumor rate and tumor age. 



We found that while in the majority of strains the differences 

 in tumor rate and tumor age remained constant in the successive 

 generations, in others certain variations became noticeable as a 

 result of the continued propagation of these strains. In a few 

 cases an increase in the tumor rate occurred in the later genera- 

 tions, but in the large majority of cases in which a change was ob- 

 served there was a tendency towards a decrease in the tumor rate 

 which in some instances was very marked. 



These changes in the tumor rate concomitant with continued 

 inbreeding seem to depend on the following two factors: (1) As a 

 result of long-continued inbreeding in mice certain characteristics 

 of a strain may change, the strain becoming less prolific and less 

 vigorous. These changes may be accompanied by a lowering in 

 the tumor rate. This was especially evident in the case of the 

 "No. 8" strain which had been inbred through the largest number 

 of generations and through a considerable number of years. (2) 

 In other cases it could be shown that in the course of continued 



1 A. E. C. Lathrop and Leo Loeb, Proceed. Soc. Biol, and Medic, 1913, XI, 34; 

 Journal of Exper. Medicine, 1915, XXII, 646, XXIII, 713. 



