PRACTICAL EXERCISES 



173 



iture, divide the sympathetic below it, and isolate it carefully with 

 fine scissors up to its junction with the vagus ganglion. 



Batteries. To setup a Daniell Cell. Fill the porous pot (Fig. 143, 

 p. 5 1 7) 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 amalga- 

 mated 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 mer- 

 cury, 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 solu- 

 tion of sulphate of 

 copper, with some 

 undissolved crystals 

 to keep it saturated. 

 After using the 

 Daniell, it must 

 always be taken down. 

 The outer pot is left 

 with the copper plate 

 and the sulphate solu- 

 tion 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 Cell contains only one liquid a mixture of r part 

 of sulphuric acid with 4 parts of a 10 per cent, solution of potassium 

 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 Leclanche 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. 



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

 arrangements as in 5(1) (p. 169), but, in addition, set up an induction 

 machine arranged for an interrupted current (Fig. 65), with a Daniell, 



FIG. 63. THE RELATIONS OF THE VAGUS IN THE 

 FROG. 



