162 THE CIRCULATION 



or hiding behind the muscles and within the cavities of the 

 body. 



34. In a few situations, however, the arteries lie near the 

 surface ; and if we apply the finger to any of these parts, we 

 shall distinctly feel a throbbing motion taking place in har- 

 mony with the heart-beat. This is part of the wave-motion 

 just mentioned, and is known as the pulse. All are familiar 

 with the pulse at the wrist, in the radial artery ; but it is not 

 peculiar to that position, for it may be felt in the carotid of 

 the neck, in the temporal at the temple, and elsewhere, espe- 

 cially near the joints. 



35. Since the heart-beat makes the pulse, whatever affects 

 the former affects the latter also. Accordingly, the pulse is 

 a good index of the state of the health, so far as the health 

 depends upon the action of the heart. It informs the physi- 

 cian of the condition of the circulation in four particulars 

 its rate, regularity, force, and fullness; and nearly every 

 disease modifies in some respect the condition of the pulse. 



FIG. 42. THE FOKM OF THE PULSE 



A very ingenious instrument, known as the sphygmograph, or 

 pulse-writer, has recently been invented, by the aid of which 

 the pulse is made to write upon paper its own signature, or 

 rather to sketch its own profile. This instrument shows with 

 great accuracy the difference between the pulses of health and 

 those of disease. In Fig. 42 is traced the form of the pulse in 

 health, which should be read from left to right. That part of 

 the trace which is nearly perpendicular coincides with the 

 contraction of the ventricles, while the wavy portion marks 

 their dilatation. (Read Note 12.) 



12. The Beating of the Pulse. "According to experiments made in 

 Paris, the pulse of a lion beats forty times a minute ; that of a tiger, 



84. Where do the arteries lie ? If we apply the finger ? Pulse ? Where felt ? 



85. The pulse as an index ? Of what does it inform the physician ? Instrument for 

 recording pulsation ? 



