CHAPTER IV 



THE BLOOD AND THE OROANS OE CIRCULATION 



Every part of the body with few exceptions is to a greater or 

 less extent vascular, that is to say, it is permeated by vessels 

 through Avhich the blood is continually circulating. The blood 

 is the medium by which nutritive substances, water, salts, and 

 oxygen are conveyed to all parts of the body, and it is through 

 this same medium that the waste products are carried away to 

 be eventually disposed of by the organs of excretion or respiration. 

 Moreover, the substances manufactured by the internally secreting 

 glands together with other chemical bodies, are likewise trans- 

 ported by the blood. Lastly, by circulating rapidly through all 

 the tissues, the blood helps to keep the temperature of the animal 

 approximately the same throughout. 





1 





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Fig. 32. Human red blood corpuscles (from Schafer). 



As seen in quantity blood is a red opaque fluid, but when 



examined in thin layers under the microscope it is found to 



consist of corjjuscles of two kinds floating in a yellowish coloured 



liquid, the blood plasma. The erythrocytes or red corpuscles 



