110 THE BLOOD AND THE LYMPH 



2 or 4 c.c. of the blood in a wide tube (of 21 mm. diameter) that has 

 been cleaned by a bichromate-acid mixture. The period that elapses 

 between the moment of the entry of fluid into the syringe and that at 

 which the clot has become firm enough so that the tube can be inverted 

 without spilling any blood, is taken as the clotting time. Since the blood 

 does not come in contact with exposed tissues, it takes from 20 to 60 

 minutes to clot by this method. 



For routine clinical examination of blood taken from a skin wound 

 Brodie and Russel's method 14 is most satisfactory. This consists in 

 principle in observing a drop of blood, under the low power of the 

 microscope, while a fine current of air is gently blown against it at 

 regular intervals in a tangential direction. Until clotting sets in, the 

 individual corpuscles move freely in a circular direction, but as soon 

 as clotting begins they move in masses which soon tend to become fixed 

 so that, although they move somewhat when the air impinges on them, 

 they immediately return to their original position when the current 

 is discontinued. When clotting is complete, the air current merely 



Fig. 20. Coaguloniett- r. The drop of blood is placed on the lower end of the glass cone and 

 the air stream is directed against it from the side tube shown by the black dot. The apparatus 

 is placed on the stage of the microscope and the drop observed by the low power. 



presses on the corpuscles at one point. By this method the clotting 

 time averages five minutes. A convenient apparatus for this method is 

 that of Boggs, which is shown in Fig. 20. It consists of a truncated 

 cone of glass, projecting into a moist chamber provided with a tube on 

 the side so arranged that when air is blown into the chamber, it strikes 

 the drop of blood placed on the end of the cone tangentially. 



Blood Clotting 1 in Certain Physiologic Conditions 



Besides the experimental conditions already enumerated as changing 

 the clotting time in the blood of laboratory animals, special mention 

 must be made of the influence of epinephrine injections, of conditions 

 supposed to cause a hypersecretion of this hormone, of the emotions, 

 and of hemorrhage. 



Epinephrine added to drawn blood does not affect the clotting time, 

 but if small amounts are injected intravenously or even subcutaneously, 

 a marked decrease occurs (Cannon and Gray; cf. Cannon, loc. cit.). 

 Larger injections may have the opposite effect, and intermediate amounts 



