1 88 THE CIRCULATION. 



to ascertain the rapidity with, which poisons introduced 

 into the blood are transmitted from one part of the vascular 

 system to another. From eighteen such experiments on 

 horses, Hering deduced that the time required for the 

 passage of a solution of ferrocyanide of potassium, mixed 

 with the blood, from one jugular vein (through the right 

 side of the heart, the pulmonary circulation, the left cavities 

 of the heart, and the general circulation) to the jugular 

 vein of the opposite side, varies from twenty to thirty 

 seconds. The same substance was transmitted from the 

 jugular vein to the great saphena in twenty seconds ; from 

 the jugular vein to the masseteric artery, in between fifteen 

 and thirty seconds ; to the facial artery, in one experiment, 

 in between ten and fifteen seconds ; in another experiment, 

 in between twenty and twenty-five seconds ; in its transit 

 from the jugular vein to the metatarsal artery, it occupied 

 between twenty and thirty seconds, and in one instance 

 more than forty seconds. The result was nearly the same 

 whatever was the rate of the heart's action. 



Poiseuille's observations accord completely with the 

 above ; and show, moreover, that when the ferrocyanide 

 is injected ( into the blood with other substances, such as 

 acetate of ammonia, or nitrate of potash (solutions of 

 which, as other experiments have shown, pass quickly 

 through capillary tubes), the passage from one jugular 

 vein to the other is effected in from eighteen to twenty- 

 four seconds ; while, if instead of these, alcohol is added, 

 the passage is not completed until from forty to forty-five 

 seconds after injection. Still greater rapidity of transit 

 has been observed by Mr. J. Blake, who found that 

 nitrate of baryta injected into the jugular vein of a horse 

 could be detected in blood drawn from the carotid artery 

 of the opposite side in from fifteen to twenty seconds after 

 the injection. In sixteen seconds a solution of nitrate of 

 potash, injected into the jugular vein of a horse, caused 

 complete arrest of the heart's action, by entering and 



