MEASUREMENT OF PULSATION BY ELECTRICITY. 63 



are affected exactly at the moment of irritation. A clear 

 idea of this will be gained by examining fig. 22, in which 

 the arrangement of the whole experiment is diagram- 

 matically represented. The muscle and the apparatus 

 represented in fig. 20 are again shown. The muscle 

 is connected with the secondary coil of the inductive 

 apparatus J\ In the primary coil J circulates a current 

 from the chain K. This current - passes through the 

 platinum plate a, and through the platinum point a\ 

 a' is attached to a lever of hard wood, a' b% and is 

 pressed by a spring against the platinum plate a. At 

 the other end of the lever is the platinum plate b\ 

 which is connected with the battery^. The other pole 

 of the battery is in connection with the galvanometer 

 g, which latter is itself connected with the quicksilver 

 capsule of the apparatus represented in fig. 20. Over, 

 but not touching, the j^latinum plate b' is the platinum 

 point 6, and this is connected with the platinum plate of 

 the same apparatus by the conductive material of the 

 key s, and of the wire k\ On pressing down the key s 

 by the handle, the platinum point b comes in contact 

 with the platinum plate b', and the current by which 

 the time is to be measured is closed. At the same 

 time, however, the end a' of the lever a^ V is raised, 

 and the current of the chain K is interrupced. This 

 produces an inductive current in the coil J"', and this 

 irritates the muscle. Irritation is, therefore, induced 

 exactly at the moment at which the time-determining 

 current is closed. 



As soon as the muscle contracts, it interrupts the 

 time-determining current. This, therefore, lasts from 

 the moment of irritation to that at which the pulsation 

 commences. In this, therefore, we measure that which 



