182 



A MANUAL OF PHYSIOLOGY 



below it, and isolate it carefully with fine scissors up to its junction 

 with the vagus ganglion. 



Batteries To set up a Daniell Cell. Fill the porous pot (Fig. 203, 

 p. 615) previously well soaked in water, with dilute sulphuric acid 

 (i part of commercial acid to 10 or 15 parts of water) to within 

 i inches of the brim, and place in it the piece of amalgamated 

 zinc. If the zinc is not properly amalgamated, leave it in the pot 

 for a minute or two to clean its surface. Then lift it out, pour over 

 it a little mercury, and rub the mercury thoroughly over it with a 

 cloth. Put the pot into the outer vessel, which contains the copper 

 plate, and is filled with a saturated solution of sulphate of copper, 



with some undis- 

 solved crystals to 

 keep it saturated. 

 After using the 

 Daniell, it must al- 

 ways be taken down. 

 The outer pot is left 

 with the copperplate 

 and the sulphate 

 solution in it. The 

 zinc is washed and 

 brushed bright. The 

 sulphuric acid is 

 poured into the 

 stock bottle, and the 

 porous pot put into 

 a large jar of water 

 to soak. 



The Bichromate 



Glass rod 



m 



J\ >* 



m '- 



\ . \ 



-17 



Vaau s ~i ' 



Cell contains only 

 one liquid a mix- 

 ture of i part of 

 sulphuric acid with 

 4 parts of a 10 per 

 cent, solution of po- 

 tassium bichromate. 

 In this is placed one, 

 or in some forms two, 

 carbon plates and a 

 plate of amalgamated 

 zinc. After using the 

 battery, take the 

 zinc out of the liquid. 



The Leclanchc battery consists of a porous pot filled with a 

 mixture of manganese dioxide and carbon packed around a carbon 

 plate, which forms the positive pole. The pot stands in an outer 

 jar of glass filled with a saturated solution of ammonium chloride, 

 into which dips an amalgamated zinc rod, which constitutes the 

 negative pole. Various forms of dry batteries can be conveniently 

 used for running induction-coils or time-markers, but are not 

 adapted for yielding constant currents of long duration. 



7. Stimulation of the Vagus in the Frog. Make the same arrange- 

 ments as in 5 (i) (p. 178), but, in addition, set up an induction 

 machine arranged for an interrupted current (Fig. 81), with a 

 Daniell, a bichromate, a Leclanche, or a dry cell in the primary 



FIG. 79. THE RELATIONS OF THE VAGUS IN THE 

 FROG. 



