SECTION IV. 

 BLOOD AND LYMPH. 



CHAPTER XXII. 



GENERAL PROPERTIES: PHYSIOLOGY OF THE 

 CORPUSCLES. 



The blood of the body is contained in a practically closed system 

 of tubes, the blood-vessels, within which it is kept circulating by the 

 force of the heart beat. It is usually spoken of as the nutritive 

 liquid of the body, but its functions may be stated more explicitly, al- 

 though still in quite general terms, by saying that it carries to the tis- 

 sues foodstuffs after they have been properly prepared by the diges- 

 tive organs ; that it transports to the tissues oxygen absorbed from 

 the air in the lungs; that it carries off from the tissues various waste 

 products formed in the processes of disassimilation ; that it is the 

 medium for the transmission of the internal secretion of certain 

 glands; and that it aids in equalizing the temperature and water 

 contents of the body. It is quite obvious, from these statements, 

 that a complete consideration of the physiological relations of the 

 blood would involve substantially a treatment of the whole subject 

 of physiology. It is proposed, therefore, in this section to treat the 

 blood in a restricted way, to consider it, in fact, as a tissue in itself, 

 and to study its composition and properties without special reference 

 to its nutritive relationship to other parts of the body. 



Histological Structure. The blood is composed of a liquid part, 

 the plasma, in which float a vast number of microscopical bodies, the 

 blood corpuscles. There are at least three different kinds of cor- 

 puscles, known respectively as the red corpuscles; the white corpus- 

 cles or leucocytes, of which in turn there are a number of different 

 kinds; and the blood plates. Blood-plasma, when obtained free 

 from corpuscles, is perfectly colorless in thin layers, for example, 

 in microscopical preparations; when seen in large quantities it shows 

 a slightly yellowish tint, the depth of color varying with different 

 animals. The red color of blood is not due, therefore, to coloration 

 of the blood-plasma, but is caused by the mass of red corpuscles held 



381 



