5i6 Journal of Comparative Neurology and Psychology. 



tion to parturition, and then again for 35 days immediately 

 after parturition. The usual length of the period of gestation 

 is from Oy to 68 days. 



The average weight of the 66 pregnant guinea pigs just 

 before delivery was 830.2 gr. Their average weight 3 days 

 after delivery was 588 gr. The average weight of unmated 

 females at that age, he had previously determined from many 

 observations to be 532. i gr. Thus it appears that at the end 

 of pregnancy, the breeding females were heavier than those not 

 allowed to breed, by about 55.9 gr. Minot's tables present- 

 ing the average alterations of weight of these 66 guinea pigs 

 from the 35 days immediately after the delivery of their young, 

 show that there is a very great loss of weight, especially mark- 

 ed during the earlier days of this period. Subsequently there 

 is a slower loss in weight continuing for about three weeks, 

 after which recovery begins. 



Owing to the destruction of Minot's pigs — the story of 

 which has become classic in the annals of American research — 

 further investigation of this subject was cut short. 



If we compare the results of EDLEFSENand Hensen's obser- 

 vations on the growth of gestating guinea pigs during their first 

 pregnancy, with those of Minot, we find a contradiction. 

 Edlefsen and Hensen conclude that the growth of the gestat- 

 ing females, when considered apart from the young developing 

 in them, is slower than that of either the unmated females or 

 males. Minot, on the contrary, concludes that the mated 

 females immediately after partuition are heavier than the corres- 

 ponding unmated females by 55.9 gr. On account of the large 

 number of animals with which Minot worked, his results are 

 probably the more reliable. 



Observations upon the Body-iveight of the White Rat. 



The writer's observations were begun upon a series of rats 

 in the spring of 1903 and were continued for approximately 

 one year. The females under observation were selected from 

 five litters of rats born in April and May of that year. The 



