CHAPTER V 



THE BLOOD 



The Hood is the common nutritive fluid of the body. Driven by the heart 

 through the vascular system in an uninterrupted stream, it supplies all parts 

 of the body with all the substances necessary for their growth and mainte- 

 nance, as well as for the combustion going on in them. Besides, the blood 

 removes from all parts of the body the greater part of the decomposition 

 products formed in the life processes, and is in its turn relieved of these 

 products during its passage through the excretory organs. 



The blood is a red, opaque fluid, somewhat heavier than water (sp. gr. 

 in man 1.057-1.066, in woman 1.053-1.061). It has a salty taste, a neutral 

 reaction, and a peculiar, stale odor. Its specific heat amounts to 0.8693 (at 

 about 38 C.). 



The blood holds its neutral reaction with the greatest tenacity. In order 

 to obtain a red coloration with phenolphthalein by addition of caustic soda to 

 the serum of ox blood, one must add seventy times as much of the alkali 

 as would be necessary if it were being added to pure water in order to obtain 

 the same reaction. The same serum mixed with methyl-orange requires three 

 hundred and twenty-seven times as much n/10 HC1 as does pure water in order 

 to bring out the red coloration. The explanation of this behavior lies in the 

 variable acid and basic character of the serum proteids (Friedenthal). 



On microscopic examination the blood is found to consist of a fluid, the 

 plasma, in which float great numbers of formed elements. These latter con- 

 stituents which cause the opacity of the blood are: (1) the red blood corpus- 

 cles to which the blood owes its red color; (2) the white corpuscles; (3) the 

 platelets. 



A few minutes (in man three to twelve) after the blood is drawn from 

 an open blood vessel it sets into a jellylike mass, which, as will be more fully 

 discussed later, is due to the fact that a proteid body present in the plasma 

 is separated out (coagulated) in the form of a solid, the so-called fibrin. 



The coagulated fibrin is a fibrous structure, which, although it amounts 

 to only 0.2-1.0 per cent of the blood, permeates and incloses in its meshes the 

 entire mass of the clot. Gradually the fibrin shrinks, in consequence of which 

 a pale yellowish fluid is pressed out. The quantity of this fluid, the serum, 

 increases progressively and finally there remains of the coagulum a smaller 

 residual mass, which consists of the fibrin, the blood corpuscles inclosed in it, 

 and the serum still present in its interstices. The blood plasma therefore 

 consists of fibrin and serum. 



11* 147 



