314 Addis 



II. The Conditions which are essential for the Accurate Estima- 

 tion OF THE Coagulation Time of the Blood by any Method. 



1. The Blood must be obtained under the same Conditions 

 in each Experiment. 



Pratt (15), using a modification of Brodie and Russell's method, con- 

 cluded that blood from deep wounds took longer to coagulate than blood 

 from superficial ones. He gives as an example a coagulation time of 7 

 minutes when the cut was deep, and of 2 minutes when it was superficial. 

 I have found that there is no appreciable difference in the coagulability 

 of blood frpm deep and from superficial punctures. 



In eight comparative observations, the average time from deep punctures 

 was 8 minutes 8 seconds, whereas, when the puncture was superficial, it 

 was 8 minutes 4 seconds. 



Several observers have stated that congestion of the part from which 

 the blood is obtained leads to a diminution of the time, the explanation 

 being that a greater quantity of coagulation-accelerating substances from 

 the tissues are added to the blood. I have not been able to confirm this. 

 Very marked congestion was produced in one arm by the application of a 

 Bier's bandage above the elbow. The average of twelve comparative esti- 

 mations of the coagulation time of blood taken from the congested fingers 

 was 8 minutes 2 seconds, while the average time of blood from the uncon- 

 gested fingers was 7 minutes 51 seconds. No conclusion can be drawn from 

 so slight a diflference as 11 seconds, because it is well within the limits of' 

 experimental error. 



Pressure near the wound while the blood is issuing has been supposed 

 to act in the same way, but again I have not been able to find that this 

 makes any appreciable difference, the average time with pressure being 8 

 minutes 5 seconds, and without pressure 8 minutes 4| seconds. 



The rate of flow of blood from the wound has proved to be of importance 

 in so far as it affects the time during which the blood is exposed to air 

 before its introduction into the apparatus. 



The other factors requisite to cause coagulation being present, air has 

 a marked influence on coagulation : its temperature is variable, and dust 

 particles no doubt attach themselves to the drop to a variable extent during 

 its exposure to air. 



The finger is the most convenient part from which to obtain blood, 

 because in it a constant size of drop and rate of outflow can be secured 

 by the employment of temporary congestion. 



In continuous haemorrhage the point of time during the course of the 

 bleeding at which a specimen is taken for examination is of considerable 

 importance. I could not use my method to demonstrate this, as exposure 

 of the blood to air leads to an increase in the agglutinability of the cor- 

 puscles. M'Gowan's method (16), modified by the addition of an apparatus 



