220 



THE BLOOD 



Jaquet chronometer. At intervals of half a minute the hair-like end 

 of a glass rod is drawn through this mixture from side to side until it 

 catches the first shreds of fibrin. This moment is again noted. Can- 

 non and MendenhalP have devised a small instrument, known as a 

 graphic coagulometer, consisting of a horizontal writing lever and a 

 vertical glass tube containing the blood to be tested (Fig. 118). A 

 coil of very thin copper wire is suspended in this blood, its other end 

 being attached to the tip of the lever. The latter is counterpoised 

 in such a manner that it retains its horizontal position without supports 

 as soon as the blood is coagulated. This procedure, therefore, con- 

 sists in releasing the lever at intervals of 30 seconds until its pointer 

 fails to rise. 



The experiments of Vierordl have shown at an early date that the 

 coagulation time of human blood is subject to considerable daily varia- 

 tions. During the morning hours, he found its value to be 9.6 minutes. 



<S- 



e 



Fig. 118. — Graphic Coagulometer. 

 A, writing lever counterpoised by weight W and supported at S and R; P, rod by- 

 means of which supports may be removed; C, wire which rests with its ring-like end; 

 D, in blood drawn into cannula C. 



after the noon-day meal 10.1 minutes, and in the evening 8.1 minutes. 

 This investigator, however, did not protect the blood against changes 

 in the temperature of the air and also failed to detect the first indica- 

 tions of clotting with any degree of accuracy. For this reason, his 

 tests have led to values which are somewhat higher than those sub- 

 mitted by other investigators. Biirker, who repeated these experi- 

 ments under more favorable circumstances, obtained values ranging 

 between 6 and 12 minutes. The latter were gotten in the morning 

 and the former in the evening. 



The coagulation time differs considerably in different individuals. 

 Hewson states that the average time is 3 to 4 minutes, while Gendrin 

 gives it as 10 minutes. Biirker, however, found a rather close agree- 

 ment, but only after he had thoroughly controlled such factors as 

 age, sex, temperature and the time of day. His values range between 

 6 and 7.5 minutes. Those of Cannon and Mendenhall average 4.9 

 minutes. The first signs of clotting usually appear within 3 or 4 

 minutes after the withdrawal of the blood. The average time in the 

 dog and cat is 2.5 to 4 minutes. 



1 Am. Jour, of Physiol., xxxiv, 1914, 225. 



