309 
May 12, 1873. 
The PRESIDENT (PROFESSOR HumPHRY) in the Chair. 
On some conditions of reflex action. By Dr M. Foster. 
Goltz observed that, while an uninjured frog, placed in a 
vessel of water the temperature of which was very gradually 
raised, made efforts to escape as soon as the water became 
warm, a brainless frog exhibited no movements, and eventually 
became rigid in the position in which it was first placed. 
Yet when a brainless frog was so suspended that the toes or 
feet only dipped into a vessel of water the temperature of 
which was gradually raised, the feet were always withdrawn 
by reflex action when the temperature reached 30° C. or there- 
abouts. ‘The slower the rise in temperature the longer was the 
withdrawal deferred, but eventually the feet were always with- 
drawn however gradual the heating of the water. When the 
whole of both legs was immersed, no withdrawal took place on 
gradual heating, and the legs became rigid without any attempt 
to escape having been made. When the legs were immersed. 
up to the knees only, the results were more or less uncertain. 
It thus appeared that when a sufficiently large surface of the 
animal was subjected to a gradual heating, reflex actions which 
otherwise would have taken place were prevented, though the 
stimulus was by the increase of surface affected largely in- 
creased. 
The absence of reflex actions in these cases cannot be 
attributed to diminution of conductivity in the motor or sensor 
nerves, or of irritability in the muscles, as these are not di- 
minished at the temperatures in question. The author was at 
first inclined to regard the facts as an example of the more 
general law of sensation that when a surface of skin is affected 
