46 HUMAN PHYSIOLOGY. 



buffed and cupped condition, on account of the aggregation of the cor- 

 puscles, and their tendency to rapid sinking. 



Nature of Coagulation. Coagulated fibrin does not preexist in the 

 blood, but is formed at the moment blood is withdrawn from the vessels. 

 According to Denis, a liquid substance, plasmine, exists in the blood, 

 which, when withdrawn from the circulation, decomposes into fibrin and 

 met-albumen. 



According to Schmidt, fibrin results from the union of fibrinoplastin 

 (paraglobulin) and fibrinogen, brought about by the presence of a third 

 substance, the fibrin ferment. 



According to Hammersten and others, the fibrin obtained from the 

 blood after coagulation, comes from the fibrinogen alone, the conversion 

 being brought about by the presence of a ferment substance, paraglobulin 

 in this case having nothing to do with the change. This view is supported 

 by the fact that the quantity of fibrin obtained from the blood is never 

 greater than the quantity of fibrinogen previously present. The origin of 

 the ferment is obscure, but there is reason to believe that it comes from the 

 injured vascular coats or from the breaking up of the white corpuscles. 



Conditions Influencing Coagulation. The process is retarded by 

 cold, retention within living vessels, neutral salts in excess, inflammatory 

 conditions of the system, imperfect aeration, exclusion from air, etc. 



It is hastened by a temperature of 1 00 F., contact with air, rough sur- 

 faces and rest. 



Blood coagulates in the body after the arrest of the circulation in the 

 course of 12 to 24 hours; local arrest of the circulation, from compression 

 or a ligature, will cause coagulation, thus preventing hemorrhages from 

 wounded vessels. 



The Composition of the Blood varies in different portions of the 

 body. The arterial differs from the venous, in being more coagulable, in 

 containing more oxygen and less carbonic acid, in having a bright scarlet 

 color, from the union of oxygen with haemoglobin; the purple hue of 

 venous blood results from the deoxidation of the coloring matter. 



The blood of the portal vein differs in constitution, according to different 

 stages of the digestive process ; during digestion it is richer in water, 

 albuminous matter and sugar ; occasionally it contains fat ; corpuscles are 

 diminished, and there is an absence of biliary substances. 



The blood of the hepatic vein contains a larger proportion of red and 

 white corpuscles ; the sugar is augmented, while albumen, fat and fibrin 

 are diminished. 



