BLOOD. 61 



ferment in the circulating blood. Just how this is done is not positively 

 known, but there is evidence that it may be due mainly to a defensive action 

 of the liver. Delezenne 1 states that when blood-serum is circulated through 

 a liver it loses its power of inducing coagulation in a coagulablc liquid, that is, 

 probably its contained fibrin ferment is altered or destroyed. It seems prob- 

 able that this action of the liver may be of importance in the normal circula- 

 tion in maintaining the non-coagulability of the blood in the living animal. 

 Moreover, injection of leucocytes sometimes diminishes instead of increasing 

 the coagulability of blood, making the so-called " negative phase " of the 

 injection. To explain this latter fact, it may be said that leucocytes give 

 rise on disintegration to a complex nucleo-proteid known as nucleo-histon. 

 Nucleo-histon in turn is said to be broken up in the circulation, with the 

 formation of a second nucleo-proteid, leuconuclein, that favors coagulation, 

 and a proteid body, histon, that has a retarding influence on coagulation. 

 The predominance of the latter substance may account for the " negative 

 phase " under the conditions described. 



Why Blood does not Clot within the Blood-vessels. — The reason 

 that blood remains fluid while in the living blood-vessels, but clots quickly 

 after being shed or after being brought into contact with a foreign substance 

 in any way, has already been stated in describing the theories of coagulation, 

 but will be restated here in more categorical form. Briefly, then, blood 

 does not clot within the blood-vessels because fibrin-ferment is not present in 

 sufficient quantities at any one time. Leucocytes and blood-plates probably 

 disintegrate here and there within the circulation, but the small amount of 

 ferment thus formed is insufficient to act upon the blood, and the ferment is 

 quickly destroyed or changed, probably by an action of the liver as stated 

 above. When blood is shed, however, the formed elements break down in 

 mass, as it were, liberating a relatively large amount of nucleo-proteids, 

 which, together with the calcium salts, produce fibrin from the fibrinogen. 



Means of Hastening" or of Retarding - Coagulation. — Blood coagulates 

 normally within a few minutes, but the process may be hastened by increasing 

 the extent of foreign surface with which it comes in contact. Tims, moving 

 the liquid when in quantity, or the application of a sponge or a handkerchief to 

 a wound, will hasten the onset of clotting. This is easily understood when it is 

 remembered that nucleo-proteids arise from the breaking down of leucocytes 

 and blood-plates, and that these corpuscles go to pieces more rapidly when in 

 contact with a dead surface. It has been proposed also to hasten clotting in 

 case of hemorrhage by the use of ferment solutions. Plot sponges or cloths 

 applied to a wound will hasten clotting, probably by accelerating the formation 

 of ferment and the chemical changes of clotting. Coagulation may be retarded 

 or be prevented altogether by a variety of means, of which the following are 

 the most important : 



1. By Cooling. — This method succeeds well only in blood that clots 

 slowly — for example, the blood of the horse or the terrapin. Blood from 

 1 Travaux <lr Physiologie, I'niversiK? do Montpellier, 1898. 



