110 ANIMAL PHYSIOLOGY. 



79. The small amount of fibrin in the liquor sanguinis, com- 

 pared with the quantity of albumen, will attract the student's 

 attention. The proportion of fibrin present varies in differ- 

 ent parts of the circulation, and it is not easy to determine 

 the measure of its variation ; but there is one circumstance 

 which makes it seem probable that the fibrin is not used for 

 the manufacture of tissue, but is a product resulting from 

 the changes effected in the blood by circulating among the 

 tissues ; and that is, that the blood emerging from the liver, 

 after being subjected to the action of that organ, is no longer 

 spontaneously coagulable, and only yields a small amount of 

 fibrin after violent whipping with rods (Beclard). 



The fibrin remains fluid while the blood circulates in tho 

 body, yet it coagulates almost immediately when withdrawn 

 from, its vessels, and still more speedily when stirred than 

 when kept at rest, unless it be kept fluid by reducing tho 

 temperature to the freezing point, or by addition of certain 

 foreign matters. This fluidity of the blood within the vessels, 

 and coagulation when removed from them, has long been a 

 puzzle to physiologists, and is not even yet fully explained. 

 But there is one point which is certain, namely, that coagula- 

 tion is the result of the mixing together of two different sub- 

 stances, both of them albuminoids, and only one of them 

 present in the liquor sanguinis, while the other, which is 

 required in comparatively very small quantity, is contained 

 in the red corpuscles. The fibrinous element of the liquor 

 sanguinis is, on this account, sometimes termed fibrinogen, 

 while the element furnished by the corpuscles, known as 

 paraglobulin, gets also the title of fibrinoplastin, or is said 

 to exercise a fibrinoplastic action. The necessity for the 

 mixing of two elements before coagulation can take placo 

 may be illustrated by tying a large vein of an ox at two 

 places, and removing the included portion filled with blood. 

 If this portion of vein be hung up, the contained blood will 

 remain fluid, but the corpuscles will fall to the bottom. If, 

 after that, the vein be opened, so as to allow the pure liquor 

 sanguinis to run out, it will be found that the liquid so 

 obtained will continue fluid for any length of time in any 

 vessel, and however much it may be stirred; but when a few 

 Ved blood corpuscles are mixed with it, it coagulates at once. 



