THE INTEGRATIVE ACTION OF THE VASCULAR SYSTEM 243 



and on occasion discharge their products into the blood 

 stream for distribution to all parts of the body. The 

 profound influence w^hich these internal secretions have on 

 the organism cannot be overemphasized. In general they 

 affect the rate and nature of the chemical changes in 

 the body, sex functions and characteristics, and the processes 

 of growth. 



We have seen that adrenin produced by the adrenal 

 medulla, when discharged in extra amount, is capable of 

 accelerating heat production. Another gland which affects 

 the speed of combustion is the thyroid, which is located 

 in the neck. When it is deficient, the processes of burning 

 in the body may be so slow that the heat output may be 

 reduced 30 per cent or more below the normal level. Natu- 

 rally enough persons afflicted with this condition are espe- 

 cially sensitive to cold weather. When the substance 

 produced by the thyroid is delivered to the blood in excess, 

 the heat production may be doubled in rate. More food 

 must be eaten in order to keep up the normal weight, the 

 skin is flushed, and sweating is prominent, for the extra 

 heat must be eliminated if normal temperature is to be 

 maintained. It is possible that the thyroid plays a role in 

 adjusting the body to alterations in the external temperature, 

 acting like the adrenal medulla but in a less ready and a 

 more persistent manner. 



The sex glands, the testes and ovary, produce substances 

 which, given into the blood stream, bring forth the typical 

 features of the male and female respectively. The influence 

 of the testes in this respect has long been known. The 

 striking transformations which occur in the boy at puberty: 

 the growth of hair on the face and other parts of the body, 

 the deeper voice, the development of physical vigor, the 

 assertiveness and sense of power, all these fail if the testes are 

 absent. Analogous changes occur in the young girl at 

 puberty and are lacking if the ovaries are removed. The 

 outer part (the cortex) of the adrenal gland also has a 

 remarkable relation to the development of superficial 

 sex appearances. If tumors of this portion of the adrenal 

 gland appear in young boys, maturing occurs at an early 

 age; the phenomenon is sometimes referred to as the 



