LECT. XVII. CIRCULATION OF BLOOD. 317 



twenty to twenty-four ; in the frog, sixty ; in birds, from 

 a hundred to a hundred and forty. Parrot ascertained 

 that his own pulse was a hundred and ten, at an elevation 

 of 4000 metres [= 13123 English feet] above the level of 

 the sea, while the number at the level of the sea, was only 

 seventy. 



Velocity of the Circulation. Let us now speak of the 

 velocity of the movement of the blood. The researches 

 made on this subject may be divided into two classes : first, 

 it is important to determine how much time the blood oc- 

 cupies in traversing the whole system ; afterwards we must 

 examine the velocity with which the blood traverses cer- 

 tain parts of this circle ; in short, with what speed it moves 

 in the arteries, the capillaries, and the veins, 



We are indebted to Hering for some of the experiments 

 on the first class of these investigations. A solution of fer- 

 rocyanide of potassium was injected into the jugular veins of 

 a horse, and at the same instant the blood which escaped from 

 the opposite jugular was collected. It was received in. num- 

 bered vessels, which were changed successively at eq.ual in- 

 intervals, by counting with a chronometer the number of 

 seconds which elapsed from the commencement of the ex- 

 periment to the moment when the blood was collected in the 

 last vessel. 



In an experiment which I had occasion to make with 

 Professor Piria, and which was performed on a horse, the 

 blood of one jugular was collected at the moment when the 

 ferrocyanide was injected into the other, and the receiver 

 was changed every five seconds. We found that the blood 

 which escaped twenty or twenty-five seconds after the in- 

 jection, contained traces of the ferrocyanide. These num- 

 bers agree with those of Poiseuille and of Hering. 



Poiseuille, when repeating these experiments, first ascer- 

 tained that, notwithstanding the introduction of the ferro- 



