66 HANDBOOK OF PHYSIOLOGY. 



Although the intimate connection of the colorless corpuscles with the 

 process of coagulation seems indubitable, for the reasons just given, the 

 exact share which they have in contributing the various fibrin factors 

 still remains uncertain. It is generally believed that the fibrin-ferment 

 at any rate is contributed by them, inasmuch as the quantity of this 

 substance obtainable from plasma bears a direct relation to the numbers 

 of colorless corpuscles which the plasma contains. Many believe that 

 the fibrinogen too is wholly or in part derived from them, and also that 

 they are the usual source of the paraglobulin present in plasma. Accord- 

 ing to this view all the fibrin factors are derived from the disintegration 

 of the colorless corpuscles. We have seen that the colored corpuscles 

 may also under certain circumstances take a share in producing the 

 fibrin generators. 



Conditions affecting Coagulation. The coagulation of the blood 

 is hastened by the following means : 



1. Moderate warmth from 100 to 120 F. (37.8-49 C.). 



2. Rest is favorable to the coagulation of blood. Blood, of which 

 the whole mass is kept in uniform motion, as when a closed vessel com- 

 pletely filled with it is constantly moved, coagulates very slowly and im- 

 perfectly. 



3. Contact with foreign matter, and especially multiplication of the 

 points of contact. Thus, as before mentioned, fibrin may be quickly ob- 

 tained from liquid blood by stirring it with a bundle of small twigs ; and 

 even in the living body the blood will coagulate upon rough bodies pro- 

 jecting into the vessels. 



4. The free access of air. Coagulation is quicker in shallow than in 

 tall and narrow vessels. 



5. The addition of less than twice the bulk of water. 



The blood last drawn is said, from being more watery, to coagulate 

 more quickly than the first. 



The coagulation of the blood is retarded, suspended, or prevented 

 by the following means : 



1. Cold retards coagulation ; and so long as blood is kept at a tem- 

 perature, 32 F. (0 0.), it will not coagulate at all. Freezing the 

 blood, of course, prevents its coagulation ; yet it will coagulate, though 

 not firmly, if thawed after being frozen ; and it will do so, even after it 

 has been frozen for several months. A higher temperature than 120 F. 

 (49 C.} retards coagulation, by coagulating the albumen of the serum, 

 and a still higher one above 56 C. prevents it altogether. 



2. The addition of water in greater proportion than tivice the bulk 

 of the blood, also the addition of syrup, glycerin, and other viscid sub- 

 stances. 



3. Contact with living tissues, and especially with the interior of a 

 living blood-vessel. 



