164 



EXPERIMENTAL PHYSIOLOGY. 



6. Varnish for Tracings. The tracing is simply drawn through 

 the varnish and then hung up to dry. 



(a.) A very good varnish consists of gum mastic dissolved 

 to saturation in methylated spirit. 



Fig. 61. Moist Chamber. N, Glass shade; E, electrodes; L, lever; W, 

 weight ; TM, time-marker ; other letters as in previous figures. 



(b.) Where a large quantity is used, and economy is an 

 object, guin juniper may be used instead of mastic. 



(c.) Dissolve 4 oz. of sandarac in 15 o/>. of alcohol, and add 

 half an oz. of chloroform. 



7. Single Contraction or Twitch Apparatus. Recording 

 drum, Daniell's cell, Morse key, induction machine, du Bois 

 key, wires, electrodes, moist chamber and lever, moist blotting- 

 paper, stout ligatures, hook, pins, lead-weight (20 grammes),, 

 frog, and the necessary instruments. 



(a.) Arrange the recording apparatus and the drum to 

 move slowly. Cover the drum with glazed paper, and after- 

 wards smoke it over a gas flame, and fix it in position. 



(b.) Arrange the apparatus as follows : One Daniell's 

 cell and a Morse key in the primary circuit, the secondary 



