HENSEL, H. 
in the cat. At constant skin temperature, we see a constant discharge 
of a certain frequency — on cooling, an increase in frequency, and 
on rewarming, an inhibition. The discharge frequency as a function 
of time during cooling and rewarming is shown in Figure 11. We 
were not able to stucfy the steady discharge of this receptor at very 
low temperatures, but I think that the maximum is to be expected 
at a temperature of about 15 C (Fig. 12). During this work we also 
found some non-specific fibers which were excited by cooling as 
well as by mechanical stimulation (Fig. 13). A sligjit pressure of 
13 grams causes a great increase in frequency and a partial adapta- 
tion. During cooling, the discharge frequency increases, whereas 
rewarming causes a transient inhibition. Mechanical stimulation 
causes a much higher increase in frequency than does rapid cooling. 
The table shows some figures found in four single non-specific 
fibers from human skin. The maximum discharge during light pres- 
sure goes up to 125 impulses/sec, but on rapid cooling only a 
maximum frequency of 17 impulses/sec is reached. Now, what is 
the sensation connected with these non-specific cutaneous fibers? I 
believe it is a mechanical sensation. This can be concluded from 
an observation made by Ernst Heinrich Weber some hundred years 
ago, that wei^ts put on the skin feel heavier when cold. This is a 
well established phenomenon and proved by several investigators. 
Any opposite experience, namely, that pressure will elicit a cold 
sensation, is not known. Thus the conclusion is justified that the 
functional significance of the non-specific receptors is a mechanical 
sensation. 
As yet, we have not found any A warm fiber in human skin. Even 
when recording from multi-fiber nerve preparations, the total dis- 
charge frequency always increased during cooling and decreased 
during rewarming (Fig. 14). Of course, it is possible that specific 
warm impulses are travelling in the C fiber group. I think it is very 
probable, but as yet we were not able to record from single C fibers 
in human subjects. 
The movie I am going to show now was made in connection with 
a television broadcast from our institute. The television company 
was kind enough to give us the whole film, from which we have cut 
a short film. It is concerned mostly with the method of recording 
afferent impulses from cutaneous nerve fibers in conscious human 
50 
