FIBRIN. 357 



blood before it has coagulated, and drying and then weighing the 

 fibrin thus separated. In the former case, notwithstanding the most 

 careful washing, the membranous cell- walls arid the nuclei (if indeed 

 they exist) of the red blood-corpuscles remain mixed with the coagu- 

 lum ; and there are also technical reasons why this method of treating 

 the blood-clot should occasion a loss of fibrin ; hence the second 

 method is generally preferred. We have already seen that fibrin 

 obtained by whipping always contains fragments of some of the 

 red corpuscles and most of the colourless corpuscles ; indeed the 

 fibrin thus obtained is far more difficult to wash, and much less 

 compact in its texture than that which is obtained from the blood- 

 clot ; it becomes somewhat reddish on exposure to the air, and 

 often begins to putrefy before it has been freed from all soluble 

 substances. The fibrin determined in quantitative analyses of blood 

 and lymph is never or very rarely free from the fat which adheres 

 most tenaciously to it. Moreover, in some forms of disease, and 

 in certain animals, the blood when allowed to stand deposits a floc- 

 culent fibrin, which on washing passes to a greater or less degree 

 through the filter. 



If the separated fibrin were always of the same consistence, and 

 if one and the same relation existed in every specimen of blood 

 between the fibrin, the fats, and the colourless corpuscles, we 

 might regard the analyses of different specimens of blood, in refer- 

 ence to the amount of fibrin, as always admitting of comparison ; 

 but we know that even under strict physiological relations, the 

 quantity of the lymph-corpuscles suspended in the blood is 

 extremely variable, and thus, for instance, we cannot strictly 

 compare analyses of the blood after repeated venesections (when 

 the blood always contains a very large number of colourless cor- 

 puscles) with those of blood not thus modified by venesection. 



Physiological Relations. 



Occurrence. The substance which on coagulation forms fibrin 

 occurs principally in the blood, in the lymph, and in the chyle. 



Its amount in normal venous blood scarcely reaches 0.3; accord- 

 ing to most observers it fluctuates between CM 9 and 0'28&. In 

 the blood of healthy men Scherer* found from 0-203 to 0'263. 

 This substance has, however, a higher importance than from its 

 small amount we should at first suppose, seeing that, in different 

 physiological and pathological conditions, its quantity is liable to 

 greater variations than that of any other constituent of the blood. 



* Haeser's Arch. Bd. 10, S._50. 



