THE PULSE. 145 



-curving ; that which, it perceives most plainly, however, is 

 the dilatation.* 



The pulse due to any given beat of the heart is not 

 perceptible at the same moment in all the arteries of the 

 body. Thus it can be felt in the carotid a very short time 

 before it is perceptible in the radial artery, and in this 

 vessel again before the dorsal artery of the foot. The 

 delay in the beat is in proportion to the distance of the 

 artery from the heart, but the difference in time between 



* For tliis fact, which is contrary to the commonly accepted doctrine, 

 1 am indebted to my friend, Dr. Hensley, who has kindly furnished me 

 with the following note on the subject : 



By determining the conditions of equilibrium of a portion of artery 

 -supposed cylindrical and filled with blood at a given pressure, it is easily 

 shown that the transverse tension is double the longitudinal. 



Also it may be shown experimentally that, if strips of equal breadth, 

 cut in the two directions from one of the larger arteries, be stretched by 

 equal weights, the stretching of the transverse slip is somewhat greater 

 than that of the longitudinal one. 



(By the word stretching is to be understood amount of stretching, and 

 not increase of length: it may be measured by the ratio ichich the 

 increase of length bears to the original length: Thus things whose 

 natural lengths are 5 and 10 inches are equally stretched -when their 

 lengths are made 6 and 12 inches respectively.) 



Such experiments also show that, within certain limits, the stretching 

 of each strip varies directly as its tension. 



Hence it will be seen that the transverse stretching of an artery, when 

 filled with blood, must be somewhat more than double its longitudinal 

 .stretching. 



This being true for different blood pressures, the difference between 

 the transverse stretchings for different pressures must be somewhat more 

 than double the difference between the corresponding longitudinal 

 stretchings ; and thus we can hardly be justified in saying that the 

 increase of longitudinal stretching which takes place with the pulse is 

 greater than the increase of transverse stretching. 



It must also be remembered that the arteries are, under all circum- 

 stances, naturally in a state of tension longitudinally, and that their 

 length, therefore, cannot be increased at all until the blood pressure is 

 increased beyond a certain point. (ED.) 



