CHAPTER III. 



THE BLOOD. 



THE blood of man, as indeed of the great majority of vertebrate 

 animals, is a more or less viscid red fluid. The exact shade of red is 

 variable, for whereas that taken from the arteries, from the left side of 

 the heart, and from the pulmonary veins, is of a bright scarlet hue, that 

 obtained from the systemic veins, from the right side of the heart, and 

 from the pulmonary artery, is of a much darker color, and varies from 

 bluish -red to reddish-black. At first sight, the red color appears to be- 

 long to the whole mass of blood, but on further examination this is 

 found not to be the case. In reality blood consists of an almost colorless 

 fluid, called Plasma or Liquor Sanguinis, in which are suspended 

 numerous minute rounded masses of protoplasm, called Blood Corpuscles, 

 which are, for the most part, colored, and it is to their presence in the 

 fluid that the red color of the blood is due. 



Even when examined in very thin layers blood is opaque, on account 

 of the different refractive powers possessed by its two constituents, viz., 

 the plasma and the corpuscles. On treatment with chloroform and other 

 reagents, however, it becomes transparent, and assumes a lake color, in 

 consequence of the coloring matter of the corpuscles having been dis- 

 charged into the plasma. The average specific gravity of blood at 60 F. 

 (15 C.) is 1055, the extremes consistent with health being 1045-1062. 

 The reaction of blood is faintly alkaline. Its temperature varies slightly, 

 the average being 100 F. (37.8 0.). The blood stream is warmed by 

 passing through the muscles, nerve centres, and glands, but is somewhat 

 cooled on traversing the capillaries of the skin. Recently drawn blood 

 has a distinct odor, which in many cases is characteristic of the animal 

 from which it has been taken. It may be further developed also by 

 adding to blood a mixture of equal parts of sulphuric acid and water. 



Quantity of the Blood. The quantity of blood in any animal 

 under normal conditions bears a pretty constant relation to the body 

 weight. The methods employed for estimating it are not so simple as 

 might at first sight be thought. For example, it would not be possible 

 to get any accurate information on the point from the amount obtained 

 by rapidly bleeding an animal to death, for then an indefinite quantity 

 would remain in the vessels, as well -as in the tissues; nor, on the other 



