118 STUDIES IN PHYSIOLOGY 



functions we have just enumerated. The alimentary canal 

 prepares the digested food, the lungs supply us with oxygen, 

 while the waste matters are excreted by the kidneys, lungs, 

 and skin. But every cell of the body, as was the case in 

 the amoeba, requires a supply of nutrients and oxygen, and 

 in every bit of living substance waste materials are being 

 constantly formed by metabolism. Since many tissues of the 

 body are at a considerable distance from the organs of diges- 

 tion, respiration, and excretion, we can see that some means 

 must be provided for bringing all these organs into commu- 

 nication with each other. This is effected by the blood, 

 which is pumped through blood vessels by the heart. In 

 this way blood is able to serve the needs of every tissue of 

 the body. 



Uses of the Blood. Blood, therefore, has four important 

 functions: (1) it carries the digested food from the alimen- 

 tary canal to the various tissues that need it; (2) it absorbs 

 oxygen in the lungs and distributes this gas to the working 

 tissues ; (3) it receives from the cells of the body the carbon 

 dioxid, water, and urea that are produced by oxidation, and 

 carries these wastes to the excretory organs, by which they 

 are thrown out of the body ; (4) it helps also to equalize the 

 temperature of the different parts of the body. 



2. A STUDY OF BEEF-BLOOD l 



Preparation. Blood is much the same in all mammals, 

 and so we can learn a great deal in regard to this important 

 tissue in our own body by studying the blood of a cow. One 

 can secure at any slaughterhouse beef-blood, which should 

 be allowed to flow from the animal into a bottle, and to stand 

 in a cold place undisturbed for several days. When first 

 drawn from the animal, it is a liquid of bright red color, but 

 it soon changes to a dark maroon. 



Blood Clot. Other changes are likewise noticeable. At 



1 See "Laboratory Exercises," No. 25. 



