94 EFFECTS OF INANITION IN THE PREGNANT ALBINO RAT. 



during the second night following delivery. This method was abandoned, however, 

 since out of a very large number of females delivering only a few became pregnant. 



(2) The second method was to place several males alone in small wire cages 

 and once each day the different females were placed with the males. If the female 

 was in heat, copulation usually took place at once. The female was not removed 

 at once, but was left with the male for a period varying from 15 minutes to an hour. 

 If not in heat, the female usually resented the advances of the male, in which case 

 ehe was removed and replaced by another female. After successful pairing with the 

 male, the female was weighed. Her weight, together with her number, was recorded, 

 and she was placed in a cage with other females that had paired. It was found 

 better to place the female in with the male, because when the process was reversed 

 the male, suddenly finding himself thrust into a strange cage, paid very scant 

 attention to the female, but would spend all his time attempting to escape from the 

 strange cage. The majority of the females were paired by this method. 



(3) The third method employed consisted in placing several males in a cage 

 with a number of females. They were left together constantly and inspected at 

 intervals of 6 hours during the day and once, in the evening. When a female in the 

 cage became in heat, the males would copulate with her with such frequency that in 

 a short time the vagina became distended, reddened, and at times would bleed 

 slightly. After a little experience, one can readily distinguish the females that have 

 copulated by the distended, reddened, and at times slightly bloody vaginal orifice. 



PERIOD AND SEVERITY OF STARVATION. 



In the beginning of the investigations it was decided to starve one group of 

 females throughout pregnancy and another group during the last half only. The 

 results from starvation were so disappointing that this part was abandoned. Of 17 

 females that had been observed to copulate and were starved from this time for 

 periods varying from 16 to 26 days, only one female gave birth to a litter, 4 of the 

 17 died, and the others were so weakened that they were saved only with difficulty. 

 In the second group 59 females were starved severely during the last half of preg- 

 nancy (or suspected pregnancy), beginning on the eleventh day after copulation. 

 The animals were weighed daily and their weights recorded. The amount of food 

 (usually not more than 1 gram) which they received daily varied with their loss in 

 weight and general condition. The food consisted of whole-wheat bread (Graham) 

 soaked in whole milk. (See table 1 for amount of food given each female during 

 starvation.) Water from the city supply was allowed in the cages at all times. 



PREVENTING THE MOTHERS FROM EATING THEIR YOUNG. 



A difficulty soon experienced was the eating of the young by the starving mothers. 

 Early in the investigation several of the mothers ate and mutilated their newborn 

 young, rendering them worthless for dissection purposes. Various muzzles were 

 devised but without success. The method finally adopted was to place the pregnant 

 female in a cage with a wire bottom, the meshes of which were 1 em. square, thus 

 allowing the newborn rats to drop through onto a clean piece of paper beneath. 

 Thus, not only were the newborns saved for dissection, but any abortions or pre- 

 mature deliveries might be noted. 



