Chemical Agents on the Nervous St/stem. 265 



Ex. 11. We prepared a frog as in fig. 4 ; and havings sus- 

 pended it with its feet in distinct glasses containing pure 

 water, as in fig. 5, passed the influence of five cells of Cruick- 

 shanks' trough, from one glass to the other, in such a man- 

 ner as that the current passed upwards in a, and downwards 

 in b. On first completing the circuit, there were energetic 

 movements in both limbs. On continuing the circuit for five 

 minutes, and breaking it, there was tetanoid rigidity in a 

 only. 



On reinstituting the circuit, the limb b was moved ener- 

 getically, and the limb a became suddenly and entirely re- 

 laxed. 



"We reversed the wires and renewed the current ; in five 

 minutes we again interrupted the current, and now the limb b 

 was affected with rigidity, and on renewing the circuit, a 

 was moved. The cui'rent was again reversed, with the same 

 reversed effect. 



If the current be reversed on breaking — a point perhaps 

 not yet perfectly established — it is always the downward cur- 

 rent which produces the marked effect of muscular action or 

 contraction. 



On removing the frog from its first position, and placing 

 it on a piece of glass, its feet resting on a plate of platinum, 

 and on connecting these, there were distinct movements of 

 the leg which had been connected with the copper end of 

 the battery, and therefore subjected to the ascending cur- 

 rent. 



Whilst the frog was still suspended, and the circuit com- 

 plete, movements took place on allowing a drop of water to 

 flow down that nerve in which the current was ascending, 

 but not in the other under the same circumstances. 



IV. Some Collateral Experiments. 



It has been already observed that if when the Voltaic cir- 

 cuit, including the lumbar nerves, see fig. 2 and 3, is com- 

 plete, and has been so for some minutes, we connect the 

 platinum wires in any part of their course, the effect, in in- 

 ducing muscular contractions is incomparably greater than 



