CHEMICAL BASIS OF THE ANIMAL BODY. 69 



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 shown by the typical facts that its activity is closely 

 dependent upon temperature, being destroyed 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 solutions (Hammarsten), produces a change which is out of all pro- 

 portion 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. Imme- 

 diately after Schmidt's discovery of the fibrin-ferment the question 

 of the existence of a myosin-ferment was investigated under his 

 guidance 1 , and resulted in the discovery of the existence in muscles 

 of an enzyme which appeared to be identical with fibrin-ferment 

 rather than specifically myosinic. The later work of the Dorpat 

 School further confirmed the above, but failed to establish the 

 existence of an enzyme, differing from fibrin-ferment and specifi- 

 cally active in promoting the clotting of muscle- plasma 2 . More 

 recently it has been shown that by applying Schmidt's method to 

 muscles which have been treated for some time with alcohol, a 

 solution may be obtained which hastens the clotting of diluted 

 muscle-plasma, does not facilitate the formation of fibrin in blood- 

 plasma and, unlike fibrin-ferment, requires to be heated to 100 

 before it loses its activity 3 . The active agent in the solution is 

 therefore not identical with fibrin-ferment and may be spoken of 

 as a myosin-ferment. 



Urea-ferment. 



When urine is exposed to the air its acidity at first increases, but 

 in most cases this speedily gives way to a marked alkalinity which is 

 accompanied by the evolution of ammonia. This is due to a hydrolytic 

 fermentative change resulting from the appearance and development in 

 the urine of certain micro-organisms of which the best known is the 



1 Michelson, Diss. Dorpat, 1872. 



2 Grubert, Diss. Dorpat, 1883. Klemptner, Ibid. Kugler, Ibid. 



3 Halliburton, Jl. of Physiol. Vol. vm. (1887), p. 159. 



