The Coagulation Time of the Blood in Man 315 



to keep the tubes at a constant temperature, showed that there was a rapid 

 and progressive diminution of the coagulation time as the haemorrhage went 

 on. Thus the coagulation time (at 18° C.) of the first blood to appear from 

 a wound was 7 minutes 15 seconds. The blood flowing from the wound 

 after 1 minute coagulated in 5 minutes 15 seconds, and after 2 minutes in 

 3 minutes 40 seconds. 



It is important, therefore, to take for examination only the first blood t(j 

 appear after a puncture. 



A comparison of coagulation times, taken when the blood was pro- 

 tected from contact with the skin by smearing the surface with lanoline 

 before the puncture was made, with the time taken in the ordinary 

 way, shows that contact with the skin for the short period which elapses 

 before the blood can be introduced into the apparatus has no appreciable 

 effect. 



On the other hand, when the skin of the part into which the puncture 

 is made is covered with recently shed blood, a very marked diminution of 

 the coagulation time results. 



This diminution no doubt results from the addition to the freshly issuing 

 blood of preformed fibrin ferment. 



It is, therefore, necessary to make sure that there are no traces of fibrin 

 ferment left on the skin, on the puncturing instrument, or on the parts of 

 the apparatus with which the blood comes in contact. 



The only certain method is by destruction of the ferment by heating 

 to a temperature above 65' C. This can be done for the apparatus. In 

 the case of the skin thorough washing in running water, with sub-sequent 

 drying by alcohol and ether is, in practice, sufficient to eliminate this fallacy. 



In connection with the method of obtaining the blood, therefore, it is 

 necessary that the skin and instruments should be clean, that the rate 

 of outflow should be approximately constant, and that the first blood which 

 appears should be taken for examination. 



2. All Estimations must be made at the same Temperature. 



The value of any method is mainly determined by its success, or want 

 of success, in maintaining a constant temperature. 



Where no attention is paid to differences of temperature the method is 

 practically worthless. The influence of even the slight variations which 

 occur in rooms, wards, or laboratories is so great as to make comparative 

 observations valueless. 



