132 THE BLOOD 



to continue their activity and the life of the individual 

 is considerably prolonged. 



Internal secretions of glands. In addition to the 

 food materials, the blood also carries the various products 

 manufactured by the different cells and organs of the 

 body. These materials, although in many cases the waste 

 products of their activity, are yet essential to the health 

 of the other organs and cells to which the blood carries 

 them. Thus the pancreas not only discharges through 

 its duct the pancreatic juice externally into the intestinal 

 tract, but also gives directly to the blood passing through 

 it an internal secretion which enables the cells of the body 

 to oxidize and utilize the sugar brought to them as food 

 by the blood. The kidney also probably does a double 

 work of supplying an internal as well as an external 

 secretion, which it gives to the blood for the benefit of the 

 rest of the body. 



Other internal secretions are those which come from 

 ductless glands such as the thyroid gland, which lies in the 

 neck; the adrenal bodies, which lie just above the kid- 

 neys ; and the pituitary body, which lies at the base of the 

 brain. These secretions have been shown by careful ex- 

 periment to be of the utmost importance to the health 

 of the other cells of the body. 



Spleen. Secretions are also probably contributed to 

 the blood by the spleen, an organ lying in the left side of 

 the abdominal cavity. Its exact functions, however, are 

 still open to dispute, since it can be removed without 

 serious consequences. The main function clearly be- 

 longing to it is the removal from the blood and the sub- 

 sequent destruction of red blood corpuscles. 



