ANIMAL CHEMISTRY. 



1. The Blood. 



As long as it flows in the veins, the blood consists of 

 a clear liquid and numberless so-called blood-corpuscles, 

 which are suspended in the liquid. The blood-cor 

 puscles are only recognizable with the aid of the micro 

 scope; they are disciform, circular, or elliptical in 

 shape, and of a yellowish-red color in all vertebrate 

 animals. The clear fluid of the blood contains, as its 

 principal ingredients, three dissolved protein com 

 pounds: albumen (serum-albumen), fibririogenous, and 

 fibrino -plastic substances. (In regard to these see pp. 

 486 and 489.) 



When drawn from the veins blood coagulates very 

 soon, the fibrinogenous and fibri no-plastic substances 

 uniting with each other to form insoluble fibrin (p. 

 489), which incloses the blood-corpuscles, and forms 

 with them an adherent, gelatinous mass, the coagulum, 

 placenta sanguinis. From this, on further shrinking, 

 the remaining solution of albumen separates as a yel- 

 lowish, almost clear, alkaline fluid, the serum, serum 

 sanguinis. Only in the case of cold-blooded animals 

 does the blood coagulate so slowly, and are the blood- 

 corpuscles so large that they can be separated from 

 the dissolved fibrin by means of filtration before the 

 coagulation. The reason why the blood remains fluid 

 in the living organism, but coagulates when no longer 

 under the influence of life, is as yet not known with 

 certainty. We only know that it is the walls of the 

 bloodvessels which prevent the coagulation in the 

 organism ; and that, outside of the animal body, the 

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