( 822 ) 



time at ail iminergiiig of tlie two legs was 10 seoomis, at an iinnierging 

 of' one leg 22 seconfls. 



It was calculated liow niiicli siilpliuric acid disappeared in the 



skin of tlie i'i\)<£, when '/i- Vo sulphuric acid ( --- 1 was used, respec- 



tivelj how much Avas fixed by the excretion-products. This occurred 

 by titrating the imnierging liquid with caustic soda (methylene orange 

 as indicator) before and after a series of 20 singular reflexes. 



Then it appears that about Vis of *''*5 total quantity of the 

 used sidphuric acid has been bound. Supposing the heat of reaction 

 of 2 aequivalents natron and I aequivalent sulphuric acid to be 

 31,4 great calories and supposing that our sulphuric acid has been 

 bound in a reaction of this kind then the heat of reaction of 

 the chemical process pro singular reflex, reckoned over the whole 

 immerged surface of the skin, amounts to 1,37 gram-calorie. It is evident 

 that only a small part of this supposed i-eaction can have taken 

 place in or near the terminations of the nerves and that this value 

 of 1,37 gram-calorie must be also a limit under which is situated 

 the heat of reaction. 



This amount may surpass the real value of the reflex-stimulus 

 perhaps a million of times. By measurijig the electrical conductivity 

 of the stimulating solution before and after the reflexes it was 

 controlled if anything else had passed into the immerging liquid 

 in the place of the disappeared sulphuric acid. This proved to 

 be the case for the increase of resistance of the liquid experi- 

 mented with, was greater than would follow from the decrease of 

 the sulphuric acid. 



§ 2. As a thermal stimulus served immersion in cold or wai'm 

 water. The most favourable i-esult was obtained by a decreasing dif- 

 ference of temperature between animal and water of 10^ C. and 

 by an increasing difference of temperature of 15° C. The reservoir, 

 isolated by an asbestos envelope, in which the immersion of the frog 

 took place contained 50 ccm. The immersion was performed once 

 and after that the reflex was waited for. Then it could be stated 

 that the temperature of the water increased on an average of 8 

 centigrades by tlie immersion of the heated frog and deci-eased on an 

 average of 22 centigrades by the immersion of the leg of a frog 

 which was conled down. Some experiments already gave a reflex 

 before it iuid come to this. A sufficient quantity of reflexes large 

 enough to avoid casualties, were accomiianied by an increase of 

 • temperature of 7 centigrades resp. a decrease of temperature of 19 



