RAPIDITY OF THE AETEEIAL CIRCULATION, 275 



remarkable degree with the experiments of Marey on the 

 form of the pulse. Marey showed that there is a marked os- 

 cillation of the blood in the vessels, due to a reaction of their 

 elastic walls, following the first violent distention by the 

 heart ; that at the time of closure of the semilunar valves, the 

 arteries experience a second, or dicrotic, distention, much less 

 than the first ; and following this, there is a gradual decline 

 in the distention until the minimum is reached. Chauveau 

 shows by experiments with his instrument, that correspond- 

 ing to the first dilatation of the vessels, the blood moves with 

 immense rapidity; following this, the current suddenly be- 

 comes nearly arrested ; this is followed by a second accelera- 

 tion in the current, less than the first ; and following this we 

 have a gradual decline in the rapidity to the time of the next- 

 pulsation. 



Rapidity in Different Parts of tlie Arterial System. 

 From the fact that the arterial system increases in capacity 

 as we recede from the heart, we should expect to find a cor- 

 responding diminution in the rapidity of the flow of blood. 

 There are, however, many circumstances, aside from simple 

 increase in the capacity of the vessels, which undoubtedly 

 modify the blood current, and render inexact any calculations 

 on purely physical principles; such as the tension of the 

 blood, the conditions of contraction or relaxation of the 

 smallest arteries, etc. It is therefore necessary to have re- 

 course to actual experiment to arrive at any definite results 

 on this point. The experiments of Yolkmann showed a great 

 difference in the rapidity of the current in the carotid and 

 metatarsal arteries, the average being 10 inches per second 

 in the carotid, to 2'2 inches in the metatarsal. The same 

 difference, though not quite as marked, was found by Chau- 

 veau between the carotid and the facial. 



The last-named observer also noted an important modifi- 

 cation in the character of the current in the smaller vessels. 

 As we recede from the central organ, the systolic impulse 



