166 CIRCULATORY SYSTEM. 



that " fat animals are found to possess less blood than leaner 

 animals ; and tame animals, which are confined, less blood than 

 wild ones." 



If we take the crassamentum (the solid clot formed by coagu- 

 lation) and wash it, we shall, by repeated ablution, deprive it of 

 its red colour, and find that we have still remaining a tough gela- 

 tinous substance ; which, when broken, exhibits a Jibrous ap- 

 pearance, and on that account has received the appropriate name 

 of 



FIBRIN. 



Some, however, call it by a name of much older date ; viz. 

 coagulable lymph. Only let us understand that both mean the 

 same thing. It may be made, artificially, to assume a more per- 

 fect fibrous aspect, by stirring the blood as it flows from the body 

 during coagulation, or by receiving it into a bottle, and shaking 

 it therein while it is congealing. In either case it will be made to 

 assume a very similar texture to muscular fibre, which it also re- 

 sembles in its chemical composition : and the resemblance maybe- 

 come so perfect, that it may seem well to merit the appellation given 

 it by the old physiologists of " liquid flesh." The similar tough- 

 ness of consistence which it acquires will not become manifest for 

 some days after its coagulation ; for I have found that the crassa- 

 mentum will continue to contract, and very gradually become 

 smaller (at the same time squeezing out serum), even for more 

 than a week from the time of the detraction of the blood. 



So singular a phenomenon as the spontaneous coagulation and 

 decomposition of the blood presents, could not fail to attract the 

 attention and consideration of those engaged in physiological pur- 

 suits ; accordingly we find various reasons assigned for it by the 

 old writers, and yet no one, even up to the present hour, has 

 been able to solve the vital problem. The two most obvious 

 changes of condition to which it is subjected are rest, and ex- 

 posure to air or cold. But, as we have just seen, it will congeal 

 though it be kept stirred or shaken in a bottle ; at the same time, 

 let it be observed, that a very brisk agitation wifl maintain its 

 fluidity : an effect arising, probably, from the natural attractive- 

 ness of the particles for each other being artificially counteracted 

 until it ceases altogether. Neither is exposure to air or a dimi- 

 nished temperature the cause, for blood will coagulate in vacuo; 

 and is, likewise, often found in clots in vessels and cavities of 

 the body, with sufficient evidence of its having been so during 

 life. So that neither of these causes will account for the coagu- 

 lation, though experiments constrain us to admit that they both 

 seem somewhat influential. 



