chap. XXL] PULSE TRACINGS. 225 



here is, that the characters are to be interpreted 

 according to the rules that have been already men- 

 tioned (page 219) as applicable to waves produced in 

 fluids by elastic tubes. For example, three tracings of 

 pulse waves are shown in Fig. 103. The tracing 

 011 the right is said to 

 be of low, that on the 

 left of high tension. 

 If we apply w T hat 



, , l l J . -, Fig. 103. Pulse Tracings. 



has been said on 



page 219, the interpretation of these two tracings 

 will be that in the latter case the elastic wall is 

 exerting great force (tension) upon the blood within 

 it, so that at each increase of pressure, with each shock 

 of the heart, little additional effect is produced upon 

 the arterial wall to distend it ; while, in the former 

 case, little force is exerted by the wall, and every in- 

 crease of pressure affects it much more considerably. 

 In other words, in the case of high tension the 

 vessel is already so distended that any additional 

 pressure only feebly affects it; or, though not dis- 

 tended, it is extensible with such difficulty that it is 

 little affected by the force of the heart. These con- 

 ditions would be produced were the blood pressure 

 very high, or, specially, if the vessel had lost its elas- 

 ticity and had become more or less inextensible, that 

 is, more nearly approaching to the condition of a rigid 

 tube. On the other hand, the condition shown in the 

 right-hand tracing is the opposite, a vessel not very full, 

 so that each increase of pressure readily affects it, and 

 specially a vessel readily distended and very elastic, 

 so that it quickly returns to its normal state of dis- 

 tension. The middle tracing shows secondary waves, 

 the condition called DICROTISM showing consider- 

 able elasticity of the arterial wall, but little force 

 of tension, a condition which could not occur in rigid 

 vessels. 



p 7 



