Chapter X 



THE INTEGRATIVE ACTION OF 

 THE VASCULAR SYSTEM 



W. B. Cannon 



A FLOWING stream of water brings to the simple 

 organisms fixed on the rocks of the stream bed the 

 food and oxygen needed for existence and carries 

 away the waste. These single-celled creatures can five only 

 in watery surroundings; if the stream dries they die or enter 

 a dormant state. The same conditions prevail for the incal- 

 culable myriads of cells which constitute our bodies. We 

 ordinarily think of ourselves as inhabitants of the air. In 

 fact, however, every part of us that is ahve is in contact with 

 fluid. The surfaces of the body are either dead, as the horny 

 layer of the skin, or are covered with moisture, as the eyes 

 and the nose and mouth. Within these surfaces are the vast 

 multitudes of minute Hving elements or cells which compose 

 our muscles, glands, brain, nerves and other parts. Each 

 cell has needs similar to those of the single cell in the flowing 

 stream. But the body cells are shut away from any chances 

 to obtain food, water and oxygen from the environment or to 

 discharge the waste materials resulting from activity. To 

 provide these necessities moving streams of fluid have been 

 developed to take from the moist surfaces of the body food, 

 water and oxygen which they dehver to the cells in the 

 remotest nooks of the organism, and from the cells they 

 bring back to the moist surfaces the useless waste to be 

 discharged. The streams which form a fluid matrix for our 

 body cells are the blood and the tissue fluid or lymph. 

 They are related to each other somewhat as the water in a 

 rivulet is related to the more stagnant water in the swamp 

 through which it flows. The blood passes rapidly along 

 fixed courses in tubular vessels; the tissue fluid, which 

 fifls the chinks and crannies outside the vessels until it too 

 is gathered in its own channels, is shifted slowly from place 

 to place. We are to examine the nature of these fluids and the 



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