BY DR. 'BURDON-SANDERSON. 301 



lation to the paper of the movement produced by the alternate 

 recession from each other, and approximation to each other, 

 of two points in the chest wall at the opposite extremities of 

 the diameter to be measured ; so that if either of these points 

 be taken as fixed, the recording of the movement of the other 

 point amounts to nothing more than the conversion of one 

 rectilinear movement into another. This is readily accom- 

 plished by the contrivance we have already employed for re- 

 cording the external cardiac movements (see 60), that is, by 

 the employment of two tympana, the one for receiving the 

 movement to be investigated, the other for inscribing it on the 

 cylinder. The receiving tympanum must be so placed that 

 the distance of its India-rubber membrane from the fixed 

 extremity of the diameter to be investigated, is subject to no 

 variation during the period of measurement, and that its ivory 

 button is applied to the movable end in such a way that the 

 diameter, if produced beyond the surface of the chest, would 

 coincide with its axis. All these conditions are completely 

 fulfilled in the instrument I use. It consists of two parallel 

 bars of iron, the opposite ends of which are screwed firmly at 

 right angles into a cross bar, so as to form a rigid frame re- 

 sembling in shape the Greek letter n. The diameter to be 

 investigated is placed between the extremities of these bars. 

 One of these carries an ivory knob, similar to that of the 

 cardiograph, the convexity of which looks towards the oppo- 

 site arm. Its distance may be varied by a screw. The other 

 arm bears the receiving tympanum, the knob of which faces 

 the knob just mentioned, their axis being in the same line. 



The mode of application of the instrument, which may be 

 conveniently called a recording stethometer, varies according 

 to the diameter to be measured. The most important diame- 

 ters are those which connect the 8th rib in the axillary line 

 with the same rib of the opposite side, the manubrium 'sterni 

 with the 3d dorsal spine, the lower end of the sternum with the 

 8th dorsal spine, and the ensiform cartilage with the 10th dor- 

 sal spine. The mode of application for the first of these diame- 

 ters is shown in fig. 247. The subject stands or sits, as is 

 most convenient, and the stethometer is hung over his neck 

 by a broad band, the length of which can be regulated by a 

 buckle. The movements recorded are not those which the 

 middle of the 8th rib performs in relation to its sternal and 

 vertebral attachments, but those which the one end of the 

 diameter executes in relation to the other, which is for the 

 moment regarded as a fixed point. In measuring the diame- 

 ters which lie in the middle plane, it is most convenient to 

 take the vertebral spines as fixed points, although, of course, 

 the results would not be affected by doing otherwise. The 

 records obtained by the stethometer are of value for two pur- 



