2. Endocrines and Populations 277 



secretion of adrenal carbohydrate-active corticoids to inhibit inflammation, 

 granulation, and antibody formation sufficiently to decrease resistance to 

 disease, although Retzlaff (1938) had indicated that there was decreased 

 resistance to infection in the subordinate mice in his population studies. 

 Experiments have been conducted which do establish these points to a 

 limited degree, but more experiments with more species are needed. 



An efficient method of inducing an inflammatory response and the forma- 

 tion of granulation tissue in rats or mice is to implant subcutaneously cotton 

 pellets moistened with turpentine (Meier et at., 1950; Christian and Wil- 

 liamson, 1958). Later these pellets and the surrounding tissue can be re- 

 moved and weighed. In this fashion the degree of the inflammatory response 

 and formation of granulation tissue can be assayed under a variety of 

 conditions. This technique has been used to show that ACTH and the 

 adrenal carbohydrate-active corticoids suppress these responses (Meier 

 ct al., 1950) . By this procedure it was found that when mice w^ere placed 

 in groups of 5 each there was approximately a 20% reduction in the amount 

 of granulation tissue formed in 1 week compared to the amount formed by 

 the segregated control mice (Christian and Williamson, 1958). These 

 experiments clearly indicated that increased population densit}^ is a suffi- 

 cient stimulus to the pituitary-adrenocortical system to decrease signifi- 

 cantly inflammation and granulation. 



Davis and Read (1958) conducted a series of related experiments in 

 which they demonstrated that placing wild-stock house mice in groups 

 markedly increased the susceptibility of the mice to invasion by the larvae 

 of TrichincUa spiralis. Each mouse was infected parenterally with approxi- 

 mately 125 embryonated Trichinella larvae. Each mouse was maintained in 

 a separate cage, but from day 3 through 11 after infection 11 of the mice 

 were placed in two groups, one of 5 and the other of 6 mice, for 3 hours a 

 day, while 11 others were left segregated. The mice were sacrificed the 15th 

 day after infection, the gastrointestinal tracts were digested, and the larval 

 worms were recovered. Only 3 of the segregated mice were infected with an 

 average of 9 worms apiece, whereas all the grouped mice were infected with 

 an average of 32 worms each, a 250% increase. The experiment was re- 

 peated with 6 segregated and 5 grouped mice, but they were not sacrificed 

 until the 30th day post infection, and the encysted larvae were recovered. 

 All the mice, segregated and grouped, were infected, but the grouped mice 

 had 48% more encysted larvae than their segregated controls. In both 

 experiments the differences in the number of worms between segregated 

 and grouped mice were highly significant and in both experiments the mean 

 adrenal weight was greater in the grouped than in the segregated mice, 8% 

 iP < 0.20) in the first experiment and 20% (P < 0.01) in the second 

 experiment. 



