THE BLOOD. 



71 



or greater numbers in the plasma, even when this has been freed from 

 colored corpuscles, have an important share in the production of the clot. 

 The proofs of this may be briefly summarized as follows: (1) That all 

 strongly coagulable fluids contain colorless corpuscles almost in direct 

 proportion to their coagulability; (2) That clots formed on foreign bodies, 

 such as needles inserted into the interior of living blood-vessels, are pre- 

 ceded by an aggregation of colorless corpuscles; (3) That plasma in 

 which the colorless corpuscles happen to be scanty, clots feebiy; (4) That 

 if horse's blood be kept in the cold, so that the corpuscles subside, it 

 will be found that the lowest stratum, containing chiefly colored cor- 

 puscles, will, if removed, clot feebly, as it contains little of the fibrin 

 faetors; whereas the colorless plasma, especially the lower layers of it in 

 which the colorless corpuscles are most numerous, will clot well, but if 

 filtered in the cold will not clot so well, indicating +hat when filtered 

 nearly free from colorless corpuscles even the plasma does not contain suffi- 

 cient of all the fibrin factors to produce thorough coagulation; (5) In a 

 drop of coagulating blood, observed under the miscroscope, the fibrin 

 fibrils are seen to start from the colorless corpuscles. 



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 

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

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

 stance obtainable from plasma bears a direct relation to the numbers of 

 colorless corpuscles which the plasma contains. Many believe that the 

 fibrinogen also is wholly or in part derived from them. 



Conditions affecting Coagulation. The coagulation of the blood 

 is hastened by the following means: 



1. Moderate warmth, from about 100 to 120 F. (37-849 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 completely 

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

 fectly. 



3. Contact with foreign matter, and especially multiplication of 

 the points of contact. Thus, coagulated fibrin may be quickly obtained 

 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 projecting 

 into the vessels; as, for example, upon threads passed through them, or 

 upon the heart's valves roughened by inflammatory deposits or calcareous 

 accumulations. 



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

 in tall and narrow vessels. 



