Electromotive Pheiiom. of the Mammal. Heart. 



259 



capillary electrometer. An image of the mercury meniscus was pro- 

 jected by means of a Zeiss C, objective and the limelight on to a slit, 

 an image of this in turn being thrown on to a moving photographic 

 plate by means of a short focus cylindrical lens. Between the lens 

 and the plate were the lever of the recording tambour, and two chro- 

 nographs, one giving a time-tracing of 8 or 100 per second according 

 to the rate of movement of the plate, and the other being in the 

 primary circuit of the 

 induction coil when ar- 

 tificial excitation was 

 used. Considerable dif- 

 ficulty was met with in 

 finding suitable electro- 

 des, since none of the 

 ordinary forms will re- 

 main in contact with 

 the heart during its vigo- 

 rous alterations in shape. 

 Brushes and threads al- 

 tered too much in re„- 

 sistance as more or less 

 of their length came in 

 contact with the sur- 

 face of the heart, and 

 the twisting of the heart gradually displaced them altogether. At 

 length we devised a modification of Hermann's nerve electrode, which 

 answered the purpose very well (Fig. 1). 



A zinc wire (Z) is well amalgamated at its lower end, which is 

 surrounded by a small bag of muslin (if) containing zinc sulphate 

 paste. Just before use a mass of normal saline paste (S) is put on 

 around the bag of zinc sulphate clay, and moulded by the fingers to 

 the form required. The zinc wire can gKde freely in a glass tube (O) 

 which is held in a clamp (A), itself freely moveable on an axis (X). 

 The whole can be adjusted in height by sliding on the upright of the 

 stand. These electrodes are so light that they follow the movements 



17* 



Fig. 1. 



