370 SCIENCE PROGRESS. 



it is cold. We now know that agitation hastens and does 

 not hinder coagulation, and that cooling hinders and does 

 not hasten the process. We have, moreover, learnt that 

 the clot contains something else in addition to the cor- 

 puscles ; this something does not exist as such in the living 

 blood, and it is of the nature of an insoluble proteid or 

 albuminous matter. It is called fibrin, and, as its name 

 implies, it consists of fibres or strings which bind the cor- 

 puscles together. The essential fact in coagulation is the for- 

 mation of fibrin, and the causes of coagulation narrow them- 

 selves down to the causes of fibrin-formation or precipitation. 



It was not until the close of the eighteenth century that 

 an idea of a coagulable substance in addition to the cor- 

 puscles was mooted ; the existence of fibrin was fully 

 recognised by Hewson (1772), and taught by Fordyce and 

 the Hunters. 



Hewson obtained specimens of blood which coagulated 

 with great slowness ; when these were allowed to stand, the 

 corpuscles settled towards the bottom of the containing 

 vessel, leaving a clear layer of plasma at the top. This he 

 skimmed from the surface, and found that after waiting a 

 short time the strands of fibrin were slowly deposited till 

 the whole fluid had set into what looked like a jelly, so 

 close were the meshes of the network. Hewson further 

 discovered the fact that cold, contact with living blood- 

 vessels, and admixture with certain neutral salts are 

 agencies which hinder or prevent coagulation by delaying 

 or preventing the deposition of fibrin filaments. In con- 

 nection with the influence of the living vessels on the 

 process, the subject was at a later stage taken up by 

 Lister, Fredericq and Brticke, who worked out many of 

 the details in connection with this inhibitory influence. 



Andrew Buchanan of Glasgow appears to be the next 

 who made noteworthy investigations on this subject. He 

 experimented with fluid obtained from the pericardial sac 

 and from the tunica vaginalis in the dropsical condition of 

 that serous membrane called hydrocele. These liquids 

 resemble blood plasma very closely, but they do not co- 

 agulate spontaneously ; Buchanan found that the addition 



