298 !*• Brailsford Robertson: 



were obtained. The development of acid in the brain as a 

 result of stimulating sensory nerves must be slight, however, 

 as an attempt to emphasise still further the difference between 

 the stimulated and unstimulated brains by rendering the Ethyl 

 Acetate faintly alkaline only resulted in the partial or complete 

 obliteration of the difference. Other indicators besides Neutral 

 Red were tried, but although differences between the stimu- 

 lated and the unstimulated brains were in some cases detected, 

 yet the most decided and invariable results were obtained when 

 Neutral Red was used. 



In connection with these experiments it should be noted 

 that a out surface must be exposed to the action of the 

 indicator and of the Ethyl Acetate, for in the case of the 

 brain the pia and in the case of muscular tissue the sarco- 

 lemma take up the stain about equally deeply whether the 

 tissue has been subjected to excitation or not. In the un- 

 stimulated brains which have been treated by the above 

 method the cut surface and the superficial connective tissue 

 are, after extraction with Ethyl Acetate, equally deeply stained, 

 the cut surface being deep pink and the connective tissue red, 

 while in the case of the unstimulated brain the cut surface 

 s almost colourless while the pia is stained red. After pro- 

 longed extraction the difference between the stimulated and 

 unstimulated brains in this respect disappears, both becoming 

 inearly colourless and much shrunken and hardened, owing to 

 the extraction of water and , consequently , of the neutral 

 Red also. 



From these considerations it appears practically certain 

 that among the products of the chemical processes 

 underlying the activity of nerve-cells is a substance 

 having the properties of an acid. 



That the increased acidity of the brain as a result of 

 Stimulation is not simply due to acid having been carried 

 thither from the tetanically contracting muscles of the body 

 by the blood-stream is shown by the fact that the development 

 of acid as a result of Stimulation is very much diminished or 

 even abolished by the previous injection into the dorsal lymph- 

 sac of a suitable dose of Esserin Sulphate which paralyses the 

 central nervous System while, on the other band, it excites 



