92 DYNAMICS OF LIVING MATTER 



such an instance in the case of contact irritability which the muscle 

 assumes when put into a solution of a decalcifying salt. As an example 

 of abnormal sensitiveness on the part of sensory nerve endings, I may 

 mention an observation on the nerve endings of the skin of a decapitated 

 frog. If such a frog be suspended vertically over a dish containing dilute 

 acid or alkali, so that the feet come in contact with the acid, they will be 

 withdrawn. If, however, the feet be dipped into a dish of pure water, 

 this will not occur; but if the feet of a frog are put for half a minute 

 or a minute into a solution of A1C1 3 or Na-citrate, and are then put back 

 into pure water, the feet are withdrawn immediately, in a most 

 violent way,* which might suggest to an anthropomorphically inclined 

 observer the idea that the contact with water caused the decapitated frog 

 the most excruciating pain. This experiment is the more surprising as 

 the contact with the sodium-citrate or aluminium-chloride solution does 

 not as a rule cause such a reaction. This hypersensitiveness of the skin 

 can be done away with by putting the feet subsequently into a normal 

 or 2 n solution of cane sugar. Urea acts similarly, but not so well. 

 I consider it possible that a number of cases of abnormal sensibility, 

 such as accompany certain neuroses, may have their basis in a change 

 in the proportion of metal proteids or soaplike compounds in a tissue. 

 As far as the action of salts on motor nerves is concerned, I have 

 made only the observation mentioned above, that those sodium salts 

 whose ions are liable to form insoluble Ca compounds are liable to cause 

 an increased irritability in a motor nerve. Mathews f has made a long 

 series of investigations on the concentration at which the various salts 

 produce rhythmical contractions when applied to a motor nerve. His 

 results practically coincide with the statements made in regard to the 

 muscles ; his interpretation, however, is different. From the fact 

 that lithium or potassium citrate causes the muscle to contract in a 

 rather low concentration when applied to the motor nerve, he concludes 

 that it is the anion which stimulates. I consider it more probable that 

 the citrate in this case acts on the Ca in the nerve in the way mentioned 

 above, and that this causes the stimulation. The formation of the Ca- 

 citrate is the essential feature, and this will occur no matter whether the 

 citrate is introduced into the muscle in the form of the sodium or lithium 

 salt. The nerve, however, differs from the muscle in that the former 

 can be stimulated through the loss of water, which is not possible in 

 the case of the muscle. It makes no difference whether the nerve loses 

 water through evaporation, or whether the water is withdrawn from the 

 muscle by a hypertonic solution. According to Mathews, cane sugar and 



* Loeb, Pfliiger's Archiv, Vol. 91, p. 248, 1902. 



t A. P. Mathews, Am. Jour. Physiology, Vol. 2, p. 455, 1904. 



