42 A CHEMICAL SIGN OF LIFE 



evidences which establish the fact that the nerve chemi- 

 cally stimulated gives off more carbon dioxide, and that 

 when rendered less excitable by reagents it produces 

 less carbon dioxide than the normal resting nerve. 



When the two sciatic nerves of a frog are isolated and 

 one is left in physiological salt solution 0.75 per cent 

 sodium chloride and the other in the body of the frog 

 for the same length of time, and when they are trans- 

 ferred to the two chambers of the apparatus, it is found, 

 if the quantities of the carbonate precipitates are com- 

 pared, that the nerve which has been in the saline solu- 

 tion produces more carbon dioxide than that which has 

 remained in the body. It is known that such a saline 

 solution raises irritability and ultimately stimulates the 

 frog's sciatic nerve. 



The different rates at which carbon dioxide is pro- 

 duced from different nerves treated by various con- 

 centrations of potassium chloride are equally instructive. 

 When a nerve is placed in a molecular solution of 

 potassium chloride, stimulation takes place for a con- 

 siderable time. Then finally the nerve becomes inex- 

 citable. But if the nerve is put in 0.2 mol. solution 

 of the same salt, nervous excitability is abolished in a 

 short time without any primary stimulation. The 

 carbon dioxide production follows exactly analogously to 

 this. The nerve treated with the stronger solution 

 gives off more carbon dioxide than the one treated 

 with the weaker solution. This was true even after 

 the nerve became inexci table, showing that the nerve 

 must still be giving off more carbon dioxide while being 

 stimulated by the stronger solution. Mr. Riggs is 

 making an extensive study of the effect of various 



