278 Dr. K. H. Alcock. On the Negative Variation [Jan. 17, 



temperature of the fixed junction took place, if it did, a correction 

 could be readily applied to the figures obtained. To guard against 

 current escape from -one circuit to another all the wires leading to the 

 nerve chamber were placed within rubber tubing, and the konstantan- 

 iron junction (A) was coated with rubber " tyre-repairing " solution, 

 which on drying left a thin and even coat of rubber on the surface, 

 insulating it from any nerve currents and from any possible mutual 

 action from or to the nerve. It was found by experiment that no such 

 action occurred. 



Fig. 6. 



To graduate the instrument the junction A was placed in melting- 

 ice, the thermo-current compensated till the galvanometer spot stood 

 at zero, and the compensator scale read off*. This was repeated with 

 hot water when it was desired to use a temperature higher 

 than the constant of B C. This graduation was performed as a 

 matter of precaution at the commencement of each day's experiments. 

 The whole apparatus proved simple and convenient to use, and of 

 an accuracy much in excess of what proved necessary in these 

 experiments. And as the junction A actually touches the nerve, there 

 can be no doubt that the actual temperature of the latter is observed. 

 The readings are given to 0*l o C. The nerve chamber was cooled by 

 being placed in a tin box, outside which was a layer of ice and salt, 



