870 PHYSIOLOGY OF DIGESTION AND SECRETION. 



tions, except perhaps that the gland is concerned in some way 

 with the processes of growth in the young animal. Formerly, it 

 was supposed that the gland reaches its maximum size at birth 

 and afterward undergoes a process of atrophy or involution, so 

 that it is entirely absent in adult hfe. Some observers claim, on 

 the contrary, that the involution of the gland does not begin 

 until after the age of puberty and that throughout life some 

 remnants of thymus tissue may be found in the masses of fat 

 which in the aclult occupy the position held by the gland in the 

 young animal. The experiments made to determine the func- 

 tions of the thymus have been conflicting and unsatisfactory in 

 their results. Injections of thymus extracts give no characteristic 

 effects, and most of the work has been concerned with the removal 

 of the gland, thymectomy, in young animals. Some observers* 

 report positive results which would indicate that the gland is 

 concerned in the regulation of the normal development of the 

 bones in the young animal and that disturbances in its functions 

 may result in the occurrence of rickets. Later and more careful 

 experiments t seem to show that such results are probably due not 

 to removal of the thymus, but to disturbances in the body 

 metabolism arising from a very serious surgical operation followed 

 by inadequate care and diet. Park and McClure, as also Tongu, 

 report that complete thymectomy is certainly not followed by the 

 death of the animal, and that, therefore, whatever functions it 

 fulfils are not essential to the life of the organism. Moreover, they 

 could detect no effect upon the growth of the bones or of the 

 body in general. In view of these negative results it may be ques- 

 tioned whether the thymus is a gland of internal secretion. Cer- 

 tainly up to the present time no conclusive evidence has been 

 furnished that it functions in this way. 



Adrenal Bodies. — The adrenal bodies — or, as they are frequently 

 called in human anatomy, the suprarenal capsules — belong to the 

 group of ductless glands. It was shown first by Brown-Sequard 

 (1856) that removal of these bodies is followed rapidly by death. 

 This result has been confirmed by many experimenters, and so far 

 as the observations go the effect of complete removal is the same 

 in all animals. The fatal effect is more rapid than in the case of 

 removal of the thyroids, death following the operation usually in 

 two to three days, or, according to some accounts, within a few 

 hours. The symptoms preceding death are great prostration, mus- 

 cular weakness, and marked diminution in vascular tone. These 

 symptoms resemble those occurring in Addison's disease in man, — 

 a disease which clinical evidence has shown to be associated with 



* Friedleben, "Die Physiologie des Thymusdriise," 1858. Klose and 

 Vogt, "Klinik u. Biologie d. Thymusdriise," 1910. Matti, "Mitt. a. d. 

 Grenzgeb. d. Med. u. Chir.," 24, 665, 1911. 



t Park and McClure, "American Journal of Diseases of Children," 18, 

 317, 1919. 



