EFFECTS OF INBREEDING ON FERTILITY AND VIGOR 



361 



Donaldson ('06) has assumed that the span of Ufe in man is 

 thirty times that of the rat, and therefore that a rat of three 

 years corresponds to a man of ninety years. Considering the 

 relatively small proportion of men that live to be nonagenarians, 

 one would not expect to find many rats in any colony living to 

 three years of age, yet under the equitable climate of California, 

 Slonaker ('12) succeeded in keeping two of a series of sixteen 

 albino rats beyond this age, and one of them lived for forty-five 

 months, or the equivalent of one hundred and twelve years of 

 human life. At various times during the past five years a number 



TABLE 12 



Showing the mortality at different ages in a group of 387 males and ^10 females 

 belonging in the seventh to the twenty-third generations of the two inbred series 

 (a combination of the data in table 10 and in table 11). Data are also shown for the 

 mortality in a series of stock albino rats comprising 199 males and 178 females 



of inbred and of stock Albinos were kept in our colony in good 

 physical condition until they were about two years old. We have 

 never attempted to keep any rats beyond this age. 



Osborne, Mendel and Ferry ('17) state that out of ninety-one 

 albino rats kept under ordinary laboratory conditions during 

 their entire lifetime, ''17 (19 per cent) died under one year of age; 

 48 (53 per cent) died between one and two years of age; and 26 

 (29 per cent) lived more than two years, the oldest one reaching 

 an age of nearly 34 months. From these figures it is evident 

 that less than a third of the rats in our colony may be expected to 

 live to be more than two years old." In another paper these 



