CHEMICAL BASIS OF THE ANIMAL BODY. 1195 



tive is sodium chloride 5 15 p.c., and permanency is attained 

 by the addition of alcohol. 



Although rennin is most copiously present in the gastric 

 mucous membrane of the calf, it may be obtained from the 

 tissue of almost any stomach, if not as ready-made enzyme at 

 least in the form of a zymogen. It occurs also in the stomach 

 of children and of man, and has been described as present in 

 the pancreas of the pig, ox and sheep. Rennin is stated to 

 occur in traces in urine. 



Fibrin-ferment. 



For ordinary purposes an extremely active ferment solution 

 may be most readily obtained by extracting the so-called 'washed 

 blood clot ' with 8 p.c. solution of sodium chloride. The solu- 

 tion in this case contains a large amount of globulins in solution, 

 as also does the similar extract which may be equally efficiently 

 prepared from ordinary washed fibrin. 



In no case as yet has the fibrin-ferment been obtained in a 

 condition of such purity as to justify any definite statement as 

 to its chemical composition. 



In addition to the undoubted relationship of leucocytes to 

 fibrin-formation it appears that the protoplasm of many other 

 cells, both animal and vegetable, may exert an influence similar 

 to that of the white corpuscles of blood. The present state of 

 knowledge and the conflicting views of various observers render 

 it impossible to make any dogmatic statement as to the origin 

 of this fibrin-ferment. 



The information which we possess as to the nature of the 

 fibrin-ferment is much less complete and satisfactory than in 

 the case of other enzymes. But that it is properly placed 

 in the class of these substances is shewn by the typical facts 

 that its activity is closely dependent upon temperature, being 

 destn^ed by heating to 70 ; that it does not affect the amount 

 but only the rate of change of fibrinogen into fibrin ; that it 

 is carried down by gelatinous precipitates formed in its solu- 

 tions, produces a change which is out of all proportion to the 

 mass of enzyme employed, and is not, so far as we know, used 

 up in the change which it induces since it is present in serum. 



Muscle-enzyme. 



The phenomena of the clotting of muscle-plasma compared 

 with those of blood-plasma and the relationship of the process 

 to the presence of neutral salts and to temperature suggest at 

 once that the change is probably one in which some enzyme 

 plays a part. Immediately after the discovery of the fibrin- 

 ferment the question of the existence of a myosin-ferment was 

 investigated and resulted in the discovery of the existence in 



