THE BLOOD. 117 



circulation of the blood with a microscope (in the mesentery 

 of the frog, for instance), we sometimes see the globules 

 bend in two, or mount, as if on horseback, the spur thrown 

 out by the bifurcation of a vessel. What is still more re- 

 markable, they may, under certain circumstances, alter their 

 shape and size, by a sort of contractility which is shown par- 

 ticularly when they are subjected to the influence of oxygen 

 gas or of carbonic acid ; the result of this change of form is 

 a change of color. When the globule is flattened and hol- 

 lowed out by the influence of oxygen, it appears brighter and 

 redder (arterial blood) ; when it is gathered, as it were, into 

 a ball, under the influence of carbonic acid, it becomes darker 

 (dark color of the venous blood). 



In a chemical point of view we notice the interesting facts 

 that the red globules contain, as mineral substances, different 

 salts from those of the liquor; that is to say, principally 

 phosphates and salts of potash, while the liquor contains 

 principally carbonates and salts of soda. We have already 

 mentioned, as one of the general properties of the living 

 globule (see part first, p. 7), its power of maintaining the 

 original composition, in spite of the laws of osmosis and 

 of diifusion. From the fact of these ingredients being found 

 in the blood globule we may infer that salts of potash would 

 be useful, instead of salts of soda, when our object is to 

 restore this particular element of the blood (in aglobulia, a 

 disease where the number of globules is diminished). 



Water in the blood globule is contained in the proportion of 

 two-thirds, a proportion inferior to that found in the globular 

 elements generally (four-fifths). The most noticeable element 



Fig. 34. Crystals of hsemin.* 



of the blood globule is an organic substance of the nature of 

 albumen, which possesses the property of crystallization. It 

 is called hemoglobin, and is composed of globulin (a com- 

 position resembling casein rather than albumen) and of 





* Obtained from the blood artificially, by the action of cooking salt and 

 acetic acid (chlorate of hematinc). 300 diam. (Virchow.) 



