322 Addis 



time was arrived at, because coagulation occurred in one tube although it 

 was not present in others until later. Considerable variations occurred in 

 the coagulation time. These were, I think, largely due to differences of 

 temperature. It is practically impossible to keep a small tin of water at 

 a constant temperature simply by adding warm water at intervals in the 

 manner recommended, especially since the observer's attention is fully 

 occupied in filling and emptying the capillary tubes. 



The 1905 method is essentially the same, except that the tubes are kept 

 at a temperature of 37° C. instead of 18"5° C. I do not think that this can 

 be regarded as an improvement. 



With this apparatus Wright (17) sometimes obtained coagulation times 

 as low as 30 seconds. I found that it took me nearly as long to fill the 

 tube and introduce it into the water. With times so short any variation in 

 the period during which the tubes are exposed to the room temperature 

 must lead to considerable error. It is in connection with the end-point, 

 however, that the most serious fallacy may be introduced. When the 

 blood is expressed on to filter paper it is difficult to see the fibrin unless it 

 is in large amount. In practice, therefore, one is apt to spread out the drop 

 or to move the pipette over the filter paper while expressing the blood. It 

 is here that the fallacy of the mechanical production of fibrin comes in, for 

 in removing the tine tube from the blood the fibrin thread which is seen 

 may not be due to coagulation at all. I think that the very low times 

 recorded by Wright (17) after the administration of calcium are to be 

 explained in this way. If the blood were not touched after it had been 

 blown out, there would be no opportunity for this error. 



Blirker's Method. 



A drop of blood from the finger is allowed to fall into a drop of distilled 

 water on a glass slide let into the lid of a box within which water at any 

 desired temperature is kept. 



Fine rods of glass are passed through the mixture of blood and water 

 every half minute until a thread or mass of fibrin is picked up. 



Biirker (21) states that the mixture of blood and water on the lid of 

 the box very quickly arrives at the same temperature as the water beneath, 

 and that variations in the temperature of the room do not materially afiect 

 the temperature of the blood mixture. Even accepting this, there is still 

 the difficulty of keeping the water at a constant temperature. I found that 

 it was impossible to keep it from varying considerably. A thermostat 

 would certainly be necessary for accurate work. Biirker (21) constructed 

 a curve showing the effect of temperature on coagulation. This was 

 compiled from only half-a-dozen observations, and as he later on described 

 considerable daily variations in the coagulation time, it is difficult to see 

 how his observations can be accepted as an accurate guide by which 

 o"bseTvations conducted at different temperatures may be made comparable. 



