BLOOD CLOTTING 111 



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 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 in Certain Physiological 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 

 may cause at first a prolongation and later a shortening of the time. 

 These results with larger doses are related to Howell's observation that 

 repeated doses of relatively large amounts of epinephrine in dogs may 

 so greatly retard coagulation as to make the animals practically hemo- 

 philic. It was further found by Cannon and his co-workers that epineph- 

 rine does not influence the clotting time when injected into animals 

 from which the abdominal viscera have been removed from the circulation 

 by ligation of the inferior vena cava and the abdominal aorta. In the light 

 of the influence which destruction of liver cells (by phosphorus, chloro- 

 form, etc.) is known to have in lengthening clotting time, it would seem 

 reasonable to conclude that it must be through this organ that epineph- 

 rine develops its clotting effects. 



Stimulation of the splanchnic nerves also shortens the clotting time, 

 and it would appear that this action depends on the resulting hyperse- 

 cretion of epinephrine (page 787), for it is not observed following stimula- 

 tion of the nerves in animals from which the adrenal glands have been 

 excised (Cannon and Mendenhall). The interesting suggestion is made 

 by Cannon that the shorter clotting time observed in animals showing 

 strong emotions of fright or fear may also be due to the hypersecretion 

 of epinephrine which this worker believes accompanies such states. 



Blood Clotting in Disease 



With the factors concerned in the process so wrapped in mystery, it is 

 not surprising that the underlying causes responsible for delayed or de- 



