THE CIRCULATING LIQUIDS OF THE BODY 41 



with difficulty intravascular coagulation. On the other 

 hand, while fibrin-ferment favours, in a high degree, the 

 clotting of blood-plasma after it has been shed, nucleo- 

 proteid is a much less efficient coagulant outside than 

 inside the vessels. There are other facts, to which we 

 shall immediately refer, which show that fibrin-ferment is 

 not precisely identical with nucleo-proteid, although it is 

 derived from it. 



Our discussion of the nature and relationships of the 

 fibrin-ferment throws light upon its source. It exists 

 only in small amount in the circulating blood ; for when 

 blood is received into alcohol direct from an artery, but 

 little ferment is found in it. In shed and clotting blood 

 the only possible sources of nucleo-proteid, so far as we 

 know, are the corpuscles and the blood-plates. The red 

 corpuscles we may at once dismiss, for although they con- 

 tain a small amount of nucleo-proteid, not only do they 

 remain intact under ordinary circumstances during coagula- 

 tion, but there is the strongest evidence, as has already 

 been pointed out, that they do not make any essential 

 contribution to the process. We have left over the leuco- 

 cytes and the platelets. The latter are said, and the former 

 are known, to yield nucleo-proteids when they are broken 

 up in the laboratory ; and it is highly probable that from 

 both, but especially from the white corpuscles, nucleo- 

 proteid is liberated in the first moments after blood is shed, 

 and that this nucleo-proteid is then changed into actual 

 fibrin-ferment. This surmise is strengthened by the fact 

 that in freshly-shed blood destruction of leucocytes and 

 blood-plates takes place ; and Hardy has shown that the 

 blood of the crayfish, which coagulates with extreme rapidity, 

 contains certain colourless corpuscles which, immediately 

 it is shed, break up with explosive suddenness, and that 

 substances which hinder the breaking up of these corpuscles 

 restrain coagulation. Further, the white layer or * buffy 

 coat ' which tops the tardily-formed clot of horse's blood 

 (Fig. 5), and consists of the lighter, and therefore more 

 slowly sinking, white corpuscles, causes clotting in other- 

 wise incoagulable liquids like hydrocele fluid, much more 



