APPARATUS FOR PHYSIOLOGICAL USE. 241 



while at some other part of its length it is supported 

 horizontally by the moving body. 



This principle is applied in a great many instruments, of 

 which the best known is Marey's sphygmograph for obtain- 

 ing records of the human pulse. In order that we may 

 see the thing in its simplicity, Mr. Page will make an 

 experiment on his own pulse. Having placed a stiff band 

 of pasteboard across the right wrist, and secured it in its 

 position by a strong indiarubber band, he takes a long light 

 lath in the other hand, and insinuates one end of it, which 

 is shaped to a chisel edge for the purpose, under the lower 

 edge of the slip of pasteboard, the opposite end of the 

 lath being extended in the direction of the arm, over the 

 palm of the hand. This done, the cardboard serves as a 



FIG. 6. Simple mode of obtaining a graphic record of the radial pulse. 



fixed axis on which the lath can rotate, and if it is so placed 

 that it rests on the pulsating artery at a very short distance 

 from the card, the extremely inconsiderable movement, 

 which is actually communicated to it by the expanding 

 artery, shows itself at the opposite end of the lath as an 

 oscillation of sufficient amplitude to be seen at any dis- 

 tance. In this way, and by means of this very simple 

 apparatus, we may obtain a tracing which exactly corre- 

 sponds to the tracing which you will see immediately 

 obtained with the sphygmograph. Let us look first at the 

 sphygmograph itself, of which, however, I can only give 

 you a very short description. It consists of a framework 

 of brass, which is capable of being fixed to the arm in such 

 a way that it is, so to speak, in one piece with the bones of 



VOL. II. B 



