The Coagulation Time of the Blood in Man 319 



ttiect of the wound on the tinie taken is slight in comparison with the 

 fffeet of the environment of the blood after it has left the wound. Any 

 method, therefore, in which the blood is not in contact with exactly the 

 same amount and kind of foreign body is likely to give erroneous results. 



4. The End-point must be Clear and Definite and must always 

 Indicate the same Degree of Coagulation. 



The various methods may be divided into two cla^sses, those in which 

 the end-point adopted is the first appearance of fibrin, and those in whicli 

 the evidence that coagulation has occurred is an indirect one deduced from 

 some change in the behaviour of the blood to its surroundings 



Thus in Wright's (17), Burker's (21), Sabrazes' (22), and M'Gowan's 

 (16) methods the coagulation time is the time elapsing from the issue of 

 the blood from the wound to the first appearance of a thread of fibrin. 



In the second class various phenomena are taken as indicating coagula- 

 tion. Thus in Hayera's (23), Milian's (24), and Brodie and Russell's (1) 

 methods change in the contour of the drop of blood is the end-point. 

 Biffi (25) and Kingston Fox (26) take the non-diffusibility of the blood 

 when introduced into water. Vierordt's (27) method depends on the fact 

 that when the blood has attained a certain degree of coagulation it no 

 longer adheres to a horse-hair. The cessation of movement of the 

 corpuscles in a film of blood under the action of gravity is the indication in 

 Buckmaster's (28) method, and in the coagulometer which I have 

 described there is a combination of the methods of both classes, for a 

 fibrinous clot is seen, and the flow of the corpuscles is stopped. 



It might be thought that the recognition of a thread of fibrin was an 

 absolutely certain proof that at least a certain amount of coagulation had 

 occurred, but even this is not sure. Buckmaster (29) has noted that 

 fibrin threads several millimetres in length may be drawn by a needle from 

 a drop of blood within 10 seconds after it has issued from the wound. 

 He takes this as an indication that coagulation is a gradual process which 

 begins whenever the blood leaves the vessels. I have very often noticed 

 the same thing when withdrawing the glass cone used in Brodie and 

 Russell's method from a drop of blood which had just appeared, and yet 

 the same drop will be found to have a normal coagulation time. It may be 

 true that coagxilation begins at once, but I do not think that it gradually 

 increases in amount up to entire coagulation, for it is a matter of common 

 experience when large quantities of blood are used that it remains 

 perfectly fluid for a time and then suddenly develops all the signs of 

 coagulation. 



If, therefore, the fine fibrin filament which can be demonstrated so early 

 indicates a certiiin amount of coagulation, it must remain very limited in 

 extent until there is a sudden crisis of coagulation throughout the whole 

 body of the blood. 



