58 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



merely dissolved albumen poor in alkali." On shaking fresh yolk with ether 

 and water, there is formed under the yellow fatty stratum of ether, a white and 

 somewhat viscid mass, which has been mistaken for Vitellin coagulated by 

 ether ; but if this substance be carefully separated by filtration and washing, it 

 is found to bear a perfect resemblance to pure casein, answering to all the casein- 

 tests (including that of rennet), and merely containing additionally a little albu- 

 men poor in salts. 1 



23. Nearly allied to Albumen, and differing from it rather in its physiological 

 than in its chemical relations, is another substance which is largely present in 

 the Human body ; namely, Globulin. This is one of the constituents of the red 

 blood-corpuscles, and is also found in the peculiar cells of the crystalline lens; 

 and is probably to be regarded as albumen somewhat changed by the peculiar 

 action of these bodies. It cannot be certainly shown to differ from Albumen 

 in ultimate composition, except that (like Casein) it contains no phosphorus; 

 but it is not coagulated by heat with nearly the same facility, whilst, on the other 

 hand, it is readily precipitated by acetic acid. In these respects, Globulin may 

 be considered as intermediate between Albumen and Casein; and it seems 

 further to correspond with the latter substance, in being quite insoluble in water 

 when detached from all k;s combinations, being only held in solution by union 

 with an alkali, or by the presence of phosphate of soda. In its coagulated 

 state, it cannot be distinguished from other protein-compounds. The quantity 

 of saline matter usually combined with globulin seems to be small ; the soluble 

 salts amounting to about 1.5 per cent, and the phosphate of lime to no more 

 than 0.25 per cent. 



24. The substance known as Fibrin is almost as closely accordant with Albu- 

 men as are the foregoing, in regard to its ultimate composition and its purely 

 chemical relations; but it differs widely in its physiological characters, which 

 are such as distinctly indicate that it possesses properties of a different nature 

 from its chemical and physical attributes, and deserving to be ranked as vital. 

 Neither Albumen, nor any other of the protein-compounds already described, 

 presents the slightest tendency to pass spontaneously into any condition that 

 presents the least trace of organization; the masses formed by their coagulation, 

 in whatever way this may have been brought about, being mere aggregations of 

 amorphous particles, entirely destitute of structure. But it is the characteristic 

 property of Fibrin, that, although existing in solution in certain animal fluids, 

 so long as they are contained within the living vessels, it tends to separate itself 

 in the solid form, that is, to coagulate spontaneously, when no longer subjected 

 to vital influence, as when withdrawn from the living body, or when the body 

 itself dies ; and, further, that the coagulum, when formed under favorable cir- 

 cumstances, exhibits a definite organic structure, of a very simple kind indeed, 

 but such as closely resembles that of tissues which form a large part of the 

 animal fabric. This substance is one, consequently, of great physiological im- 

 portance. It is found in all fluids that are being applied to the nutrition of 

 living tissues, or are in immediate preparation for that purpose : thus it is one 

 of the most characteristic ingredients of the Blood; it also presents itself in 

 Chyle and Lymph; and it is a component of all those exudations which are 

 designated as "plastic," from their tendency to give origin to new tissues. On 

 the other hand, it is entirely absent from all the normal secreted fluids, whether 

 these are destined for special uses within the body, or are to be carried forth 

 and discharged as the products of its decay. All these circumstances seem to 

 point very decidedly to the conclusion, that Fibrin is to be considered as a 

 hutoffenetic substance in the act of conversion into living tissue, its molecules 

 having a tendency to assume one of the peculiar arrangements which is charac- 



"Lehrbucli der physiologischen Chemie," Band ii. p. 349. 



