704 STUDIES IN GENERAL PHYSIOLOGY 



nerve behaves in exactly the opposite way from the muscle. 

 The latter contracts when taken out of the solution and ex- 

 posed to the air, and relaxes when put back into the solution. 

 If the nerve alone (without the muscle) be put into the 

 solution, contractions of the muscles occur while the nerve is 

 in the solution, and partial or complete relaxation is observed 

 when the nerve is taken out. 



These experiments on the nerve give one the impression 

 that the sodium-citrate solution and the solutions of the 

 other sodium salts whose anions precipitate calcium stimu- 

 late the nerve chemically. Albert Mathews has recently 

 found that weak solutions of sodium salts can cause con- 

 tractions of the muscle when the nerve alone is put into the 

 solution, while the salts of the other metals can only produce 

 contractions when their osmotic pressure is considerably 

 higher than that of the tissues. I have confined my experi- 

 ments chiefly to those sodium salts whose anions precipitate 

 calcium. But I think I can show definitely that these salts 

 are not the direct stimulus that calls forth the contractions 

 of the muscle, but play only an indirect role, inasmuch as 

 they make the nerve more sensitive for another kind of 

 stimulus, either a mechanical- or a contact-stimulus. When 

 the nerve alone has been put into a sodium-citrate solution 

 (of 1 gram-molecule in about 10 liters) and the muscle has 

 begun to contract powerfully, a gradual relaxation of the 

 muscle is observed when the nerve is taken out of the solu- 

 tion and allowed to hang in the air. But at any time the 

 contractions and the final tetanus of the muscle will begin 

 again when the nerve is brought into contact with any solid 

 or liquid body, no matter whether it is a conductor or a non- 

 conductor. As soon as the contact ceases and the nerve is 

 surrounded by air again on all sides the muscle gradually 

 relaxes. This can be repeated quite often with the same 

 result. Among the substances whose contact causes con- 



