THE BLOOD. 165 



istics. It is insoluble in water and in solutions of sodium chlo- 

 ride; insoluble in hydrochloric acid, though it swells in this 

 menstruum. 



It may be whipped out from the freshly shed blood by a 

 bundle of twigs, wires, or other similar arrangement presenting 

 a considerable extent of surface; and when washed free from 

 red blood-cells presents itself as a white, stringy, tough sub- 

 stance, admirably adapted to retain anything entangled in its 

 meshes. If fibrin does not exist in the plasma, or does not arise 

 directly as such in the clot, it must have some antecedents al- 

 ready existing as its immediate factors in the plasma, either 

 before or after it is shed. 



The principal theoi'ies of coagulation are these : 1. Coagu- 

 lation results from the action of a fibrin-ferment on fibrinogen 

 and paraglobulin. 2. Coagulation results from the action of 

 a fibrin-ferment on fibrinogen alone. Fibrinogen and para-, 

 globulin (see sections on " The Chemistry of the Animal Body") 

 are proteids originating from the plasma, during clotting in all 

 probability. Fibrin-ferment loses its properties on boiling, and 

 a very small quantity sufQces in most cases to induce the result. 

 For these and other reasons this agent has been classed among 

 bodies known as unorganized ferments, which are distinguished 

 by the following properties : 



They exert their influence only under well-defined circum- 

 stances, among which is a certain narrow range of tempera- 

 ture, about blood-heat being most favorable for their action. 

 They do not seem to enter themselves into the resulting prod- 

 uct, but act from without, as it were (catalytic action), hence a 

 very small quantity suffices to effect the result. In all cases 

 they are destroyed by boiling, though they bear exposure for 

 a limited period to a freezing temperature. 



From observations, microscopic and other, it has been con- 

 cluded that the corpuscles play an important part in coagula- 

 tion by furnishing the flbrin-ferment ; but the greatest diver- 

 sity of opinion prevails as to which one of the morphological 

 elements of the blood furnishes the ferment, for each one of 

 them has been advocated as the exclusive source of this fer- 

 ment by different observers. 



We do not favor the current theories of the coagulation of 

 the blood. We would explain the whole matter somewhat thus : 

 What the blood is in chemical composition and other properties 

 from moment to moment is the result of the complicated inter- 



