42 



Scientific Proceedings (36). 



recorded. Changes in excitability were observed by stimulating 

 with the middle pairs of electrodes. 



B. The vagus nerves of spreading vipers were isolated and 

 stationary electrodes placed beneath each nerve. The heart (apex) 

 was connected with a lever by means of a thread and its action 

 recorded. After establishing the control responses to vagal stimu- 

 lation by leading a current through each pair of electrodes con- 

 secutively, a saturated solution of magnesium sulphate, mag- 

 nesium chloride, sodium sulphate, sodium chloride, calcium 

 chloride or cane sugar was applied to the nerves below the elec- 

 trodes and the nerves again stimulated, the nerves being washed 

 with 0.75 per cent, sodium chloride and normal response estab- 

 lished between each application. 



Results. — 1. The direct application of strong solutions of 

 magnesium sulphate to a mixed nerve (sciatic) is, as a rule, soon 

 followed by contraction of the muscles supplied by the nerve ; 

 and often by contraction of the muscles of the opposite leg, as well 

 as other muscles of the body (reflex contraction). 



2. Stimulation of the nerve above and below the point to 

 which the salt is applied gives results indicating the onset of 

 afferent before efferent block. 



3. If the salt be removed soon enough the block may dis- 

 appear. 



4. Other substances, e. g., sodium chloride, sodium sulphate, 

 magnesium chloride, calcium chloride, or cane sugar, give similar 

 results. 



5. In common with all the other above mentioned substances 

 tried the application directly to the vagus nerve of a strong solu- 

 tion of magnesium sulphate or magnesium chloride causes a loss 

 in conductivity in the cardiac-inhibitory fibers ; and if the solution 

 be removed soon enough conductivity may be restored. 



We do not consider that any specific action of strong mag- 

 nesium salts solutions on the conductivity of nerve fibers has 

 been made out. The blocking effect does not appear to differ 

 from that produced by any markedly hypertonic solution. 



