CONTROL OF THE CIRCULATION. 8 1 



larger veins. So the constant slight differences in com- 

 position of the blood and lymph in the various tissues are 

 counterbalanced by the mingling of the currents from 

 these various parts in the large arteries and veins. 



The Spleen. The function, or functions, of the spleen are not well 

 understood. It is believed to have something to do with the renova- 

 tion of the blood, perhaps forming colorless corpuscles and destroying 

 colored corpuscles. At any rate, the physiologists generally call it a 

 blood gland. It is unlike true glands in that it has no duct, and forms 

 no secretion to be poured into any cavity, like the glands of excretion 

 and secretion. It has been found, in the case of accidents to man, and 

 by experiment on the lower animals, that life may continue after this 

 organ has been removed. 



Massage. A system of pressing, rubbing, and knead- 

 ing the muscles is known as massage. It helps the flow 

 of the blood and lymph, thus aiding in washing out the 

 waste products from the muscles and other parts of the 

 body that are to be reached by pressure. We have seen 

 that one of the benefits of exercise is to promote the cir- 

 culation of the blood and of the lymph, and so to help 

 get rid of the waste matters that are produced by the 

 activity of the various organs. Many invalids cannot take 

 active exercise. So this passive exercise may very fairly 

 take its place, and assist in the nutrition of the tissue by 

 accelerating the flow of blood and lymph, bringing new 

 nourishment and carrying away wastes. For students 

 who do not take sufficient exercise it is a good thing to 

 rub the body thoroughly and briskly, not only after a 

 bath, but often with the hands or with a dry towel. 



Transfusion of Blood. Transfusion of blood is the transfer of 

 blood from the blood vessels of one animal to those of another. Trans- 

 fusion may be direct or immediate, as when the blood vessels of the 

 two animals are connected by tubing so that the blood passes from one 

 to the other without exposure to the air ; in indirect or mediate trans- 



