318 NUMBER OF PULSATIONS. LECT. XVII. 



cyanide, neither the number of pulsations, nor the force of 

 the heart's contractions varied. But, like Hering, he dis- 

 covered traces of the ferrocyanide in from twenty or twenty- 

 five seconds after its introduction. 



I cannot refrain from relating some of Poiseuille's experi- 

 ments, made for the purpose of ascertaining the influence 

 which certain substances mixed with the blood had on the 

 velocity of its circulation. He found in every case, that 

 the number of pulsations, and the force of the contractions, 

 were unaltered. When a solution of acetate of ammonia 

 was injected along with the ferrocyanide the latter was de- 

 tected in about eighteen seconds; and nitrate of potash 

 gave an analogous result, but extending this interval to 

 twenty seconds. On the contrary, when a little alcohol was 

 added to the ferrocyanide injected into the jugulars, the 

 latter did not escape from the opposite vessel until after 

 forty or forty-five seconds. The influence of these sub- 

 stances upon the rapidity of the circulation merits especial 

 attention, for it is connected with a fact entirely within the 

 domain of molecular physics. Poiseuille ascertained, in an 

 important investigation on the passage of water, serum, &c., 

 in capillary tubes, that these substances acted there abso- 

 lutely in the same way as in the sanguineous circulation. 

 It is not, however, to be supposed that it is by this kind of 

 influence that many other substances introduced into the 

 blood, act; for a great number of them exercise their in- 

 fluence upon the nervous force, and through this on the 

 contraction of the muscular fibre of the heart. Thus, a 

 small quantity of an infusion of coffee injected into the 

 veins of a dog, instantly augments the force of the heart's 

 contraction, while a solution of opium diminishes its energy. 



The rapidity of the circulation, that is, the time which 

 a molecule of blood occupies in passing from the right to 

 the left ventricle, seems, at first sight, to have been very 



