FIBRIN. 19 



taste and odour, and is insoluble in water, alcohol, and ether. 

 When placed in water it sinks ; it speedily absorbs a portion 

 of the fluid, swells up, assumes its original bulk, and increases 

 its weight threefold. 



The composition of fibrin is represented by the formula' 

 C,opH3,,N,, O,,,, SP, orlOPr + SP. 



The observ^ations which have been made respecting the action 

 of acids and alkalies on protein apply equally to fibrin. 



Fibrin is stated to have the power of decomposing binoxide of 

 hydrogen catalytically with the evolution of oxygen and heat. 

 According to Scherer this action is induced by fresh fibrin 

 from any source, but not by boiled fibrin. This power is not 

 possessed by albumen. 



A concentrated solution of nitrate of potash dissolves humid 

 fibrin in the course of twenty-four hours, and gives it the pro- 

 perties of albumen. (Denis.) This observation requires further 

 confirmation ; it has failed in the hands of Simon and other 

 chemists, and it is not impossible that the phenomena described 

 by Denis were due to the presence of some uncombined potash. 



The average quantity of fat associated with fibrin was found 

 by Simon to vary from 2 to 4^, which agrees closely with the 

 results of other observers. 



Fibrin always contains a certain amount of salts, especially 

 of the phosphate and sulphate of lime : the former seems to be 

 chemically combined with it. The amount, according to Simon, 

 lies between 1-5 and 2^. 



Diagnosis of fibrin. Fibrin is distinguished by its spontaneous 

 coagulation, by its insolubility in water, alcohol, and ether, and 

 by its precipitation from acid solutions by ferrocyanide and 

 ferridcyanide of potassium. 



4. Casein. 



This substance constitutes the most important ingredient in 

 the milk of the mammalia. We have already shown that it 

 also exists in vegetables. 



Casein mav be obtained with facility bv either of the following 

 methods. 



' See Appendix I, Note 8. 



