CHAPTER VII 

 A STUDY OF THE BLOOD 



1. USES OF THE BLOOD 



Nutrition in the Amoeba. The process of nutrition in the 

 amoeba is relatively simple. When the single cell, by push- 

 ing out its false feet, comes in contact with a bit of food, 

 the protoplasm of the animal slowly flows about the food 



FIG. 42. An Amoeba taking in a Particle of Food. 



particle until the latter is surrounded. Once within the 

 cell, the food is digested by the living substance, and, as 

 the animal is continually altering its shape, this digested 

 food is easily moved from one part of the cell to another. 

 The animal is so small it has no need of a specially devel- 

 oped alimentary canal or blood system. Oxygen is absorbed 

 by the protoplasm as fast as it is needed, and the waste 

 matters (carbon dioxid, water, and urea), that are always 

 formed in living substance, are given off by the amoeba as 

 fast as they are produced. Every part of the cell may be 

 said to perform the functions of mouth, stomach, and intes- 

 tine, of blood, respiratory, and excretory systems. 



Nutrition in Man. In the human body, on the other 

 hand, we find special organs, each devoted to but one of the 



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