( 823 ) 



centigrades. Consequently at these last experiments a quantity of 

 beat of 3,5 gr. calorie must have been withdrawn from ihe leg of 

 the frog, and 9,5 calorie have been added. This heat divided itself 

 during a reflex-time of average 7'/^ sec. resp. 9 sec. over the whole 

 immerged part of the skin. Only a veij small part will have come 

 to the benefit of the terminations of the nerves and what appears 

 as a reflex-stimulus may very well be millions of times smaller than 

 the total quantity of the heat which is given or taken up. The 

 above mentioned values have again only the significance of limit 

 values beneath which the heat resp. cold stimulus, which causes a 

 reflex movement, must be necessarily situated. 



§ 3. To produce mechanical reilex-stimuli first falling mercury 

 drops were made use of ^), afterwards a little ball of resin fastened 

 to a pig's-bristle, which by an electrically moved tuning fork of 

 16 double vibrations was kept in a forced vibration of fixed ampli- 

 tude. In both cases as much as possible the lateral side of the 

 foot, where the corpuscula tactus are situated, was taken. 



The mercury drops were all of the same size (average 100 mgr.) 

 and were used to the number of 1 to 15, trickling down one after 

 the other. The iieiglit from which the drops were falling varied 

 from i to 20 cm. At each experiment the vis viva was calculated 

 with which the drop came down on the skin of the animal. It was 

 obvious that for causing a reflex the vis viva had to be in minimo 

 686 ergs which aniount was obtained by dropping 7 drops one after 

 the other from a falling height of 1 cm. Once it was possible to 

 obtain a reflex by the fall of one drop from a height of 7 cm. 

 which shows the same quantity of energy now contained in one 

 single stimulus without any summation. 



The smallest results according to vis viva Avhich still produce 

 a reflex were obtained with a little ball of resin of 7 milligram 

 which vibrated with an excursion of 5 mm. After a retlextime of 

 on an average 3 sec. the reflex movement was obtahied. The 

 quantity of energy which was added to the skin in this way in 

 summing contains 212 ergs. 



The result of the mechanical stimulation is quantitatively consi- 

 derably lower than the above mentioned chemical and caloric 

 stimulation. It leads to a mininuim, which however put together 

 in a rt'strici sjiol still [)ossesses the peculiarity of having been 

 communicated to a part of the skin which probably is considerably 



'; E. A. ScHAFER, Proc. Physiol. Soc. 26 Jan. "901. 



