2. Endocrines and Populations 271 



It has been established that close confinement with adequate feeding can 

 result in adrenocortical atrophy and lymphoid hypertrophy in a variety of 

 species of mammals (Christian and Ratcliffe, 1952), but these limits of 

 confinement evidently were not approached in the above experiments, as 

 indicated by the adrenal weights in the large and small cages. 



These results apply to male mice. When female mice are grouped, there 

 is evidence of increased adrenocortical activity, increased corticoids and 

 androgens being secreted (Christian, 1960). The degree of hypertrophy is 

 small, however being nowhere nearly the amount seen in grouped male mice 

 or even in females from populations of mixed sex. The inference is that the 

 cortical hypertrophy seen in females from populations of mixed sex must to 

 a large degree reflect a situation created primarily by the males. 



3. Food and Social Competition; Splenic Hypertrophy 



In all the experiments with mice so far discussed, food and water were 

 provided ad libitum. Food was scattered over the cage and water was 

 available from several sources in order to avoid competition for food which 

 might result in inanition in the subordinate animals and might constitute 

 stimuli to the endocrine adaptive responses. These precautions were taken 

 even though observation had indicated that feeding and drinking were 

 more or less random and on an individual basis, and that there was no 

 observable competition for these items. Also Uhrich (1938) and Strecker 

 and Emlen (1953) had indicated that a limited supply of food did not in- 

 crease competition among house mice. Nevertheless, the question whether 

 or not the location and amount of food was a major factor in eliciting the 

 observed changes in grouped mice in the pituitary-adrenal and pituitary- 

 gonadal systems was answered by specifically designed experiments. In 

 one series of experiments, male mice, some in groups of four each and some 

 segregated, were provided food either ad libitum or limited to 4.0 gm. per 

 mouse per day for a 7-day experimental period. This amount of food re- 

 stricted weight gain but did not produce weight loss. The food given the 

 grouped animals, whether limited or ad libitum, was scattered for half of 

 the populations and supplied from a feeder for the other half. Therefore 

 food was given the mice in one of the four following ways: scattered and 

 limited in amounts, from a feeder and limited, scattered and ad libitum, or 

 from a feeder ad libitum. The experiment was repeated using groups of 

 five each and a food limitation of 3.5 gm. per mouse per day, an amount 

 which produced an appreciable weight loss in all the mice during the week 

 of the experiment. This amount of food per mouse per day can therefore be 

 said to produce inanition. It was found that neither the location of food, 

 whether scattered or from a feeder, nor the amount of food had any effect 



