THE VASCULAR GLANDS. 11 



development and growth of the bod} 7 , the most abundant supply of highly 

 organized blood is necessary. The bulk of the thymus gland, in propor- 

 tion to that of the body, appears to bear almost a direct proportion to the 

 activity of the body's development and growth, and when, at the period 

 of puberty, the development of the body may be said to be complete, the 

 gland wastes, and finally disappears. The thyroid gland and supra-renal 

 capsules, also, though they probably never cease to discharge some amount 

 of function, yet are proportionally much smaller in childhood than in foetal 

 life and infancy; and with the years advancing to the adult period, they 

 diminish yet more in proportionate size and apparent activity of function. 

 The spleen more nearly retains its proportionate size, and enlarges nearly 

 as the whole body does. 



The vascular glands seem not essential to life, at least not in the 

 adult. The thymus wastes and disappears: no signs of illness attend some 

 of the diseases which wholly destroy the structure of the thyroid gland;- 

 and the spleen has been often removed in animals, and in a few instances 

 in men, without any evident ill-consequence. It is possible that, in such 

 cases, some compensation for the loss of one of the organs may be afforded 

 by an increased activity of function in those that remain. 



Although the functions of all the vascular glands may be similar, in 

 so far as they may all alike serve for the elaboration and maintenance of 

 the blood, yet each of them probably discharges a peculiar office, in rela- 

 tion either to the whole economy, or to that of some othef organ. Re- 

 specting the special office of the thyroid gland, nothing reasonable can be 

 suggested; nor is there any certain evidence concerning that of the supra- 

 renal capsules. Bergman believed that they formed part of the sympa- 

 thetic nervous system from the richness of their nervous supply. Kolliker 

 states that he is inclined to look upon the two parts as functionally dis- 

 tinct, the cortical part belonging to the blood vascular system, and the 

 medullary to the nervous system. 



