ACTIVITY OF THE ALBINO RAT 35 



the general conclusion that the greatest percentage of gain in 

 weight is made soon after birth and this percentage of increase 

 diminishes rapidly during the first month of life. 



Minot 3 has found that in the growth of rabbits the average 

 daily gain up to five days of age is 1 7.6 % for the males and 16% 

 for the females. At the age of from 25 to 30 days the gain had 

 dropped for the males to 5.3% and for the females to 6.8% . In 

 the case of the growth of the chicken the average daily increase 

 drops from about 9% on the fifth day to about 5% on the 

 thirtieth day. He found a somewhat similar condition to obtain 

 in the guineapig. 4 



Donaldson 5 in speaking of the growth of man says " * * * 

 from birth to the first year there has been an increase in weight 

 of 240% for the males, and 190% in the females. But this 

 rate diminishes during the succeeding years with astonishing 

 rapidity." 



Miller 6 in a paper on the Norway rat has found that the 

 male is 52 mm. long and the female is 49 mm. at 

 birth. The average weight of both sexes at birth was 

 found to be 6.4 grams. There was a gain of from 1/7 to 1/10 

 in 24 hours. By the seventh day they had doubled their weight; 

 by the eleventh day they had trebled it; by the fifteenth, they 

 had quadrupled it ; and by the seventieth day they had reached 

 an average weight of 115 grams, or 18 times their weight at 

 birth. This is somewhat heavier than the average albino rat, 

 but no doubt the same relative increase would occur during 

 the first month. The average weight of the albino rat at the 

 age of 70 days, according to Table IV, is 84 grams. 



In order to determine the growth the rats were weighed 

 before feeding at intervals of about two weeks. This was often 

 enough to show the changes in weight during the life time. It 

 was found that the changes in weight were fairly gradual and 

 that weights taken at greater intervals would be sufficient. 

 Accordingly the weights which were made about a month apart 

 were selected in constructing Table IV. Figs. 13 and 14 were 



3 Minot, C. S. The problem of age, growth and death. 1907, pp. 254 and 258. 



4 Minot, C. S. Senescence and rejuvenation. First paper— On the weight of 

 guinea pigs. Jour, of Physiol., vol. 12, 1891, pp. 98-153. 



5 Donaldson, H. H. The growth of the brain, p. 02. 



• 6 Miller, Newton. Reproduction in the brown rat. (Mus. Norwegicus). Amer. 

 Nat. 1911. vol. 45, pp. 023-035. 



