CHAPTER V. 



THE BLOOD 



THE blood is. ; to be considered from a certain standpoint as a fluid 

 tissue; it consists of a transparent liquid, the blood-plasma, in which 

 a vast number of solid particles, the red and white blood-corpuscles (and 

 the blood-plates), are suspended. 



Outside of the organism the blood, as is well known, coagulates more 

 or less quickly; but this coagulation is accomplished generally in a 

 few minutes after leaving the body. All varieties of blood do not coagulate 

 with the same degree of rapidity. Some coagulate more quickly, others 

 more slowly. In vertebrates with nucleated blood-corpuscles (birds, 

 reptiles, batrachia, and fishes) DELEZENNE has shown that the blood 

 coagulates very slowly if it is collected under such precautions that it 

 does not come in contact with the tissues. On contact with the tissues or 

 with their extracts it coagulates in a few minutes. The blood with 

 non-nucleated blood-corpuscles (mammals), on the contrary, coagulates 

 very rapidly. The coagulation of the blood in these cases may also be 

 somewhat retarded by preventing the blood from coming in contact 

 with the tissues (SPANGARO, ARTHtis 1 ). Among the varieties of blood 

 of mammals thus far investigated the blood of the horse coagulates most 

 slowly. The coagulation may be more or less retarded by quickly cool- 

 ing; and if we allow equine blood to flow directly from the vein into a 

 glass cylinder which is not too wide and which has been cooled, and let it 

 stand at C., the blood may be kept fluid for several days. An upper 

 amber-yellow layer of plasma gradually separates from a lower red layer 

 composed of blood-corpuscles with only a little plasma. Between these 

 is observed a whitish-gray layer which consists of white blood-corpuscles* 



The plasma thus obtained and filtered is a clear amber-yellow alkaline 

 (toward litmus) liquid which remains fluid for some time when kept 

 at C., but soon coagulates at the ordinary temperature. 



The coagulation of the blood may be prevented in other ways. After 

 the injection of peptone, or, more correctly, proteose solutions into 



1 Delezenne, Compt. rend. soc. de biol., 49; Spangaro, Arch. ital. de Biol., 32; 

 Arthus, Journ. de Physiol. et Pathol., 4. 



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