60 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



position leads to the development of ammonia, carbonic acid, butyric acid, and 

 sulphuretted hydrogen, and leaves a residue consisting principally of leucine and 

 tyrosine ( 19). It was long since pointed out by Denis, 1 that spontaneously- 

 coagulated fibrin may also be reduced to a condition closely resembling that of 

 albumen, by the action of nitrate of potash (this action, as is justly remarked 

 by Lehmann, not being one of mere solution, but of transformation); and it 

 has been since ascertained by Zimmermann, that various saline solutions will 

 have the same effect upon fibrin digested in them. 2 Although there is much 

 discrepancy in the evidence on this point, yet on the whole it seems that the 

 fibrin of venous blood is thus taken up more readily than the fibrin of arterial 

 blood, or than fibrin which has been exposed for some time to the air; and that 

 exposure to the air has the effect of precipitating the dissolved protein-compound 

 in fine flocks; thus indicating that arterial fibrin is in a state of higher oxida- 

 tion than venous fibrin, and is further removed from the state of albumen. 

 The solution thus obtained coagulates in flakes at the temperature of about 162 ; 

 but it differs from an albuminous solution in being strongly precipitated by acetic 

 acid; whilst, on the other hand, it is not coagulated by ether, as is true fibrin 

 in solution. When Fibrin is boiled, moreover, it is converted into a substance 

 which can scarcely be distinguished chemically from coagulated albumen; and 

 this operation prevents it from being converted into a soluble albumen-like sub- 

 stance by digestion in saline solutions. By continued boiling, however, with 

 free exposure to the air, its character is further changed ; and it is converted 

 into the substance termed by Mulder tritoxide of protein ( 29), which may also 

 be obtained by treating albumen in the same manner. Thus all the means 

 which tend to bring back Fibrin to the condition of a mere chemical compound, 

 by destroying that peculiar molecular arrangement which its particles have 

 acquired, tends to reproduce in it the properties of ordinary Albumen. Like 

 Albumen, moreover, Fibrin is always in a state of intimate union with fatty 

 substances; about 2 per cent, of these being usually associated with it. 

 Mineral substances, especially phosphate of lime, also present themselves in its 

 ash; but usually in smaller proportion than in that of albumen. 



26. The process of solidification of Fibrin, as ordinarily seen in the coagula- 

 tion of the Blood when drawn from the vessels of the living body, is somewhat 

 complicated by the presence of the corpuscles which are floating in the fibrinous 

 fluid ; and it can be better watched when these corpuscles have been separated 

 from it, either by filtration, or by subsidence. Thus when the coagulation takes 

 place at an unusually long interval after the blood has been drawn (as com- 

 monly happens in the case of inflammatory blood), the red corpuscles sink 

 towards the bottom, in virtue of their higher specific gravity, and the fibrinous 

 fluid is left free from them ; and the same end may be obtained by covering the 

 blood with a layer of oil, which, by excluding the atmosphere, retards its coagu- 

 lation ; or by treating it wifch dilute solutions of alkaline sulphates, nitrates, &c., 

 which have a similar retarding effect. The first indication of the approaching 

 change, as seen with a microscope in a thin film, consists in the appearance of 

 minute molecular points, which are scattered over the field; and from these 

 speedily arise fine thread-like prolongations, which radiate irregularly from 

 them, crossing those that arise from other centres, and at last covering the 

 whole field of view as with a delicate but somewhat irregular cobweb. This 

 fibrillation seems to bear a certain analogy to crystallization, being the result of 

 forces which tend to withdraw the solid particles from their state of solution in 

 the liquid, and to bring them together in a certain definite mode of aggregation ; 

 and there are certain peculiarities in the process, which to some extent bear out 



1 "Arch. g6n. de Med.," 3ieme Ser. torn. i. p. 171. 

 8 "Casper's Wochensckrift," No. 30, 1843. 



