XXXTV.] 



THE OKAPHTC WITHOD. 



197 



5. Muscle-Lever (change in length of muscle). — It is customary 

 to use such a muscle-lever as is shown in fig. 116, with the weiglit 

 attached directly under the point of attachment of the muscle to 

 the lever. This has its disadvantages, as it is set into vibration by 

 the rapid rise of the lever. Fick has shown that by using a light 

 straw lever, the muscle itself being made tense not by a weight 

 applied directly under the point of attachment of the muscle to 

 the lever, but by attaching the weight over a small pulley fixed 

 to the steel axis to which the lever is attached, by this arrange- 

 ment the weight is raised but little, and even with a rapid con- 

 traction does not move quickly. 



Fig. 116.— Moist Chamber. N. Glass shade; E. Electrodes; L. Lever; W. Weight) 

 TM. Time-marker ; other letters as in previous figures. 



6. Moist Chamber (fig. 116). — To prevent a preparation from 

 getting dry, enclose it in a moist chamber, which is merely a glass 

 shade placed over the preparation. To keep the air and the pre- 

 paration moist, cover the sides of the shade with blotting-paper 

 moistened with normal saline. 



7. Varnish for Tracings. — ^The tracing is drawn through the varnish and 

 then hung up to dry. 



(a.) A good varnish consists of gum mastic or white shellac dissolved to 

 saturation in methylated spirit. 



(Ik) Where a large quantity is used, and economy is an object, gum juniper 

 may be used instead of mastic. 



(c. ) Dissolve 4 oz. of sandarac in 15 oz. of alcohol, and add half an oz. of 

 chloroform,' 



8. Single Contraction or Twitch.— Apparatus. — Recording 

 drum, Daniell's cell, Hg-key, induction coil, Du Bois key, wires, 



