250 /. /. Christian 



marked in the thymus. The greater sensitivity of thymocytes over the 

 l3'mphocytes of the lymph nodes and spleen may be due to their greater 

 rate of proliferation. Hydrocortisone is more effective in involuting lymph- 

 oid tissue than cortisone or corticosterone and tends to produce degenera- 

 tive changes among immature lymphocytes of the lymph nodes to a much 

 greater degree than cortisone (Dougherty, 1953; Santisteban and Dough- 

 erty, 1954) . On the other hand, pituitary growth hormone and deoxycorti- 

 costerone appear to promote the growth of lymphoid tissue. The apparent 

 increase in lymphoid tissue in gonadectomized or adrcnalectomized animals 

 (or in those animals with adrenocortical atrophy from inactivity or over- 

 feeding) (Christian and Ratcliffe, 1952) apparently results from protection 

 against involuting agents rather than a true hyperplasia (Dougherty, 

 1953; Santisteban and Dougherty, 1954) . 



The thymus is also involuted by androgens, estrogens, and to a variable 

 degree by thyroidectomy (Weaver, 1955) ; androgens also potentiate the 

 ability of the carbohydrate-active corticoids to effect thymic involution 

 (Selye, 1955; Dorfman and Shipley, 1956) . The cortex and medulla remain 

 as distinct zones after this type of in\'olution, although they are less clearly 

 defined than in normal (Weaver, 1955). All elements of the thymus share 

 equally in the involutional process. Thymocytes are reduced, but no acute 

 destructive changes are noted. Therefore involution of the thymus by sex 

 hormones is a nonspecific action (Weaver, 1955) . The so-called involution 

 due to aging of the thymus is prevented by gonadectomy in either sex 

 (Selye, 1947) ; it is therefore logical to assume that the normal involution 

 of this gland, seen especially at puberty (Christian, 1956) , is due to the sex 

 steroids. 



It should be clear that thymic mvolution, and therefore thymic weight, 

 can be a useful index of adrenocortical activity providing adequate con- 

 sideration is taken of the action of the sex steroids. 



h. Lymph node weight is a useful index of adrenocortical activity as their 

 lymphoid tissue is involuted by adrenal corticoids as discussed above, but 

 to a less marked degree than for the tlwmus (Weaver, 1955). The iliac 

 lymph nodes are involuted by prolonged administration of ACTH, acute 

 administration of cortisone (Weaver, 1955), or a variety of stimuli evoking 

 increased adrenocortical activity, but the sex steroids or thyroidectomy are 

 without effect on the lymph nodes (Weaver, 1955) or maj^ even cause a 

 hypertrophy of the nodes (Money et al., 1950) . A weight loss of the lymph 

 nodes should therefore more specifically reflect increased adrenocortical 

 activity than the thymus. However, tlwmic weight, properly controlled, is 

 more frequently used because of its much greater sensitivity to the carbo- 

 hydrate-active corticoids. Selye (1950) has indicated that the lymph nodes 



