THE NORMAL ACTIVITY OF THE ALBINO RAT FROM 



BIRTH TO NATURAL DEATH, ITS RATE OF 



GROWTH AND THE DURATION OF LIFE 



JAMES ROLLIN SLONAKKK 

 From the Physiological Laboratory of Stanford University 



Fourteen figures 



INTRODUCTION 



The purpose of this experiment was to ascertain the norma* 

 activity of the albino rat from birth to death due to old age, 

 its rate of growth, and the duration of life. From previous 

 experiments J it was seen that to reach these results a number 

 of rats of the same age and parentage should be used. To pro- 

 cure such material female rats of the same litter were segregated 

 and mated to the same male. After a number of trials lasting 

 over a year two sister rats, having been mated to the same 

 male, gave birth to an equal number of young just a day apart. 

 It was of great importance to have the young rats as nearly 

 alike as possible. Previous observations have shown that 

 prenatal and postnatal conditions greatly affect the rate of 

 growth and activity. 4 For example, when the conditions of 

 parentage were as nearly alike as possible the young of a litter 

 of three would have a decided advantage over those of a litter 

 of eight. That is, the individuals of the smaller litter were not 

 only a trifle larger at birth but also grew much faster due to 

 the fact that each received more nourishment than was possible 

 in the larger litter. Since the young had to be nourished by 

 the mother until they were old enough to wean it was deemed 

 very important that not only should the mothers be as nearly 

 alike and related as possible, but that each litter should be of 

 the same number and age. With this material in hand condi- 

 tions were as nearly ideal as it was possible to obtain. 



In selecting the young for the experiment an equal number 

 of each sex should be used, but owing to the fact that the ex- 

 ternal sexual characters are not easily distinguishable at the 

 weaning time it was not possible to secure this ideal condition. 



Eight young were selected from the two litters. They were 

 arranged and designated in the following manner: i and 2 

 from litter A; 3 and 4 from litter B; 9 and 10 from A; and 11 

 and 12 from B. Numbers 1 to 4 inclusive were placed in revolv- 



1 Slonaker, J. R. The normal activity of the white rat at different ages. Jour. 

 Comp. Neurol, and Psychol., 1907, vol. 17, pp. 342-359. 



20 



