160 



THE SIGNS OF LIFE 



at regular intervals. In this class of observations, a speed of 2^ to 

 5 mm. per minute is usually sufficient. The " lost time " of nerve- 

 skin reaction is a good instance of a phenomenon fitted for the 

 galvanometric record, e.g., Figs. 28 and 43. 



It is convenient to adopt a standard size of recording plate ; the 

 "quarter plate" in England, and the 9 by 12 on the Continent, 

 answer all ordinary purposes. These dimensions enable us to 

 record a series of deflections with an amplitude varying from 

 i to 5 cm., and a length of at least 10 cm. The speeds named 



FlG. 63. Galvanograph and Railway Myograph. 



give records lasting 40 and 20 minutes ; 5 mm. per second gives 

 a 20 seconds record. For speeds above 5 mm. per second a record- 

 ing electrometer should be used. 



Simultaneous records. In certain cases it is desirable to obtain 

 the simultaneous record of a series of electrical reactions and of the 

 corresponding series of muscular contractions. 



For this purpose, a truck carrying a smoked plate, and con- 

 nected with the suspended carrier that holds the photographic 

 plate, is added to the apparatus. The thread by which the carrier 

 is suspended passes round the axis of the motor and over two small 

 pulleys, and is fastened to the carrier of the smoked plate, 



