HENSEL, H. 
DR. HENSEL: We did not measure conduction velocities of cold 
fibers using cold stimulation but only be electrical stimuli. We can 
be absolutely sure that the impulse set up by the electrical stimulus 
is identical with that caused by cold in the respective single fiber. 
The fiber can be identified by the characteristic shape of the impulse 
and by the collision technique shown in Figure 4. 
DR. FREEMAN: How does the latency compare with A fibers 
in this technique? 
DR. HENSEL: You mean the latency between the stimulus and 
the onset of the impulses? 
DR. FREEMAN: No, using this technique for measuring the 
conduction velocity and the duration of the impulse and its height. 
How do your figures for these C fibers compare with your observa- 
tions of A fibers under the same circumstances? 
DR. HENSEL: Well, I would say that the latency of the A fibers 
is about 1/30 to 1/50 of that of the C fibers. 
DR. STUART: Are the frequency spectra for pressure and 
temperature change in a single C fiber always different? 
DR. HENSEL: I am not sure about that. Recently we found a 
non-specific fiber which was quite as sensitive to cooling as the 
specific cold fibers. 
DR. CLARK: I think in one of your figures you said something 
about on and off potentials. Is that "off "due to the thermode change, 
or was it a real on and off effect? 
DR. HENSEL: I think it is a real on and off effect. The over- 
shoot in frequency during the onset of cooling is the mirror image 
of the false start during onset of rewarming. In some records, the 
whole course of the false start is not seen, as the impulse frequency 
cannot drop below zero. 
DR. CLARK: That is on all your records except one? 
60 
