272 J. J. Christian 



on adrenal weight in the segregated or grouped mice. (Irouping produced 

 significant adrenal and splenic hypertrophy along with atrophy of the 

 thymus and reproductive organs, and these changes were not altered by 

 the source or amount of food. The splenic hypertrophy produced in the 

 albino house mice in these experiments by grouping paralleled the splenic 

 hypertrophy in voles following social "stress" (Clarke, 1953; Chitty et at., 

 1956). However, restricting the amount of food resulted in an atrophy of 

 the reproductive organs, thymus, and spleen which was related to the 

 degree of food restriction. The source of food was without effect on the 

 adrenals, thymus, spleen, or reproductive organs. Therefore the source or 

 amount of food did not increase the level of social competition above that 

 already present as a result of the establishment of a social order. The 

 amount of food provided had no effect on the adrenal glands, therefore it 

 was concluded from these and the experiments of others (Mulinos and 

 Pomerantz, 1941; D'Angelo ct al., 1948; Baker, 1952) that inanition does 

 not constitute a stimulus to the pituitary-adrenocortical system of house 

 mice and rats. 



On the other hand, Frank's (1953) experiments with confined popula- 

 tions of meadow voles (Microtus arvalis) suggest that a deficient supply of 

 food may increase social competition in this species, as a marked increase 

 in fighting occurred following the development of a food shortage. Whether 

 or not a food shortage will increase competition very likely depends on the 

 time relationships of the feeding behavior of the species. One would not 

 expect to find increased competition among animals which feed randomly 

 with respect to time, otherwise one would have to attribute to these animals 

 the ability to predict, ahead of time, the development of a shortage, as 

 there would be no appreciable increase in competition for food at any given 

 moment. This consideration also implies that dominant and subordinate 

 animals would lose weight equally in the presence of a deficient food supply. 

 Such was actually the case in the experiments with house mice (Christian, 

 1959c) . On the other hand, an increase in competition would be expected to 

 follow the development of a food shortage among mammals which habi- 

 tually feed during the same period of time every day. In this situation one 

 would not expect the dominant animals to lose weight to the same degree 

 as the subordinate animals, if at all. Frank's (1953) results coincide with 

 this latter situation. If these conjectures are correct, it is apparent that the 

 temporal feeding relationship and behavior of any species will assume para- 

 mount importance with respect to the production of competition and the 

 physiologic responses to it, and should therefore be investigated critically 

 for a variety of mammals. The experiments with house mice should be re- 

 peated with voles and other species and any increases in competition deter- 

 mined by observation and the accompanying adrenocortical responses. 



