CHAPTER IV. 



THE BLOOD. 



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

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

 red is variable, for whereas that taken from the arteries, from the left 

 side of the heart or from the pulmonary veins, is of a bright scarlet hue, 

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

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

 bluish-red to reddish-black. To the naked eye, the red color appears to 

 belong to the whole mass of blood, but on examination with the micro- 

 scope it is found that this is not the case. By the aid of this instrument 

 the blood is shown to consist in reality of an almost colorless fluid, called 

 Liquor Sanguinis or Plasma, in which are suspended numerous minute 

 rounded masses of protoplasm, called Blood Corpuscles. The corpuscles 

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

 these means., discharged 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 temper- 

 ature varies within narrow limits, the average being 100 F. (37 '8 C.). 

 The blood stream is slightly warmed by passing through the muscles, 

 nerve centres, and glands, but is somewhat cooled on traversing the capil- 

 laries 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; the odor may be further developed 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 



