274 CIRCULATION. 



of the needle are carefully noted, as they occur with the sys- 

 tole of the heart, with the diastole, etc. After withdrawing 

 the instrument, it is applied to a tube of the size of the ar- 

 tery, and we measure the rapidity of the cm-rent required to 

 carry the needle to the points noted, which may be done by 

 the same calculation used in graduating the apparatus of 

 Yierordt, 1 



This instrument is on the same principle as the one con- 

 structed by Yierordt, but in sensitiveness and accuracy is 

 much superior. In the hands of Chauveau, the results, par- 

 ticularly those with regard to variations in the rapidity of 

 the current, are very interesting. 



Rapidity of the Current in the Carotid. It has been 

 found that three currents, with different degrees of rapidity, 

 may be distinguished in the carotid : 



1. At each ventricular systole, we have, as the average 

 of the experiments of Chauveau, the blood moving in the 

 carotids at the rate of twenty T 4 inches per second. After 

 this the rapidity quickly diminishes, the needle returning 

 quite or nearly to zero, which would indicate complete 

 arrest. 



2. Immediately succeeding the ventricular systole, we have 

 a second impulse given to the blood, which is synchronous 

 with the closure of the semilunar valves, the blood moving 

 at the rate of eight -^ inches per second. This Chauveau 

 calls the dicrotic impulse. 



3. After the dicrotic impulse, the rapidity of the current 

 gradually diminishes, until, just before the systole of the 

 heart, it becomes almost nil. The average rate after the di- 

 crotic impulse \&five -$ inches per second. 



These experiments give us, for the first time, correct no- 

 tions of the rapidity and variations of the flow of blood in 

 the larger vessels ; and it is seen that they correspond in a 



1 In graduating the apparatus, Chauveau uses warm water. It would be 

 more accurate to use defibrinated blood, or a fluid of equal density. 



