MEASUREMENTS 



263 



this book is always, in principle, similar to Marey s tanbour or 

 tympan (vide 5) . The movement caused by the heart, the pulse, 

 or the respirations, etc., induces corresponding movements in an 

 elastic membrane. The motion of the latter is transmitted pneu- 

 matically to a similar tambour, which acts upon a stylus, by means 

 of which the movement can be 

 recorded, and also, if desired, 

 magnified. Examples of such 

 instruments are the sphygmo- 

 graph, the cardiograph, the pneu- 

 mograph, etc. 



Fig. 147 shows Marey ''s cardio 

 graph which is used to record the 

 pulsations of the heart. An 

 ivory button S is fitted in con- 

 tact with the membrane, as 



FIG. 14? 



Marey's Cardiograph. 



shown, against which it is pressed by means of a spiral spring, 

 the tension of which can be regulated by the screw V. The 

 apparatus is applied to the chest, so that the button, S, is against 

 the heart, at about the fifth intercostal space, and the pressure of 

 the air is transmitted to a recording tambour. 



The pneumograph shows 

 the rise and fall of the 

 chest. Laulanie's model 

 has a tympan, T, soldered 

 to a piece of metal which is 

 applied to the chest. An in- 

 extensible ribbon, R, passes 

 round the chest and is fixed 

 to the metal at A, and to 

 the teeth, B, of a jointed 

 plate P. This plate receives 

 the button of the membrane 

 and stretches it by means 

 Pneumograph. of the lever L, and the elastic 



strap 1. It is easy to understand that in inspiration the plate is 

 pushed at B and tends to rock, pulling on the membrane, from 

 which an aspiration of air is transmitted to the receiving typman. 

 The contrary takes place in expiration (fig. 148) . Double pneumo- 

 graphs are also used. Fig. 137 shows a pneumographic record 

 being made during work. 



Marey's sphygmograph shows the pulsation or the pulse, that 

 is to say, the pressure of the flow of blood in the radial artery. 



In fig. 149 a spring holds a little ivory disc against the artery 

 and slightly compresses it, and the oscillations of the disc are 

 transmitted to a rocking member B, which acts on the membrane 



iff 



