APPENDIX I. 115 



a curve, traces a vertical line (s s f in Fig. 2) corre- 

 sponding to the two limbs of the curve, the ascending 

 and the descending one, which have coalesced. 



A very essential precaution in these, as well as in 

 all experiments on nerves or muscles, is that these 

 textures, especially the nerves, should be carefully 

 preserved from becoming dry. This can be done 

 by covering the part of the apparatus containing 

 them with a shade, the inner walls of which are 

 lined with moist bibulous paper ; or, as was the 

 case on the present occasion, by enclosing the nerve 

 in a tube of vulcanite, in which it rests on two pairs 

 of platinum electrodes, one as near to, the other as 

 far from, the muscle as possible. This tube of 

 vulcanite is also provided with another contrivance, 

 which will be more fully mentioned presently. 



The speaker now proceeded to show a complete 

 experiment with the spring-myographion. After 

 two curves had been traced, one by stimulating the 

 nerve near to, the other by stimulating it far from, 

 the muscle, the magnified image of the curves was 

 exhibited to the audience by means of the electric 

 light. 



Conditions upon which the rate of Propagation of the 

 Nervous Agent has leen hitherto found to depend. 

 1. The figures given above (see pages 104 and 110) 

 for the rate of propagation of the nervous agent were 

 obtained at a temperature of from 11 to 21 C. At 

 a lower temperature, Professor Helmholtz found the 

 velocity was greatly diminished.* This can easily 

 * Joh. Muller's Archiv, u. s. w., 1850, 8. 358. 



