318 REPORTS ON THE STATE OF SCIENCE, 
excitation. We have, therefore, as a general conclusion covering the 
three cases of muscle, nerve, and skin that the effect of moderate heat 1s 
anti-excitatory. 
And we may refer back to the negative answers given to the question 
whether thermic shocks can act as stimuli to-muscle. Obviously the 
fact that ‘thermic shocks’ give upon muscle and nerve electrical 
effects in opposite direction to that of the effects of excitation—t.e., in 
an anti-excitatory direction—is in harmony with the conclusion that 
they do not act as stimuli to either muscle or nerve. The phenomena 
of heat-paralysis, moreover, which are apparently entirely non-exci- 
tatory, are in equal harmony with the conclusion.* 
Similar experiments upon plants give results similar to those 
obtained upon muscle and nerve—i.e., zincativity in consequence of local 
injury and local excitation ; anti-zincativity in consequence of moderate 
local warmth. So far the identity of electrical effects in the case of 
animal and vegetable tissues is complete. The points on which identity 
is not complete relate (1) to the question of transmission, and (2) the 
question whether thermic shocks act as plant stimuli. We do not feel 
prepared to give a firm answer to this second question. On the side 
of a negative answer we have the fact that the electrical effect of 
moderate heat is in the anti-excitatory direction. On the other hand, 
the facts concerning transmission in which ‘thermic excitation’ was 
employed appear to imply an affirmative answer. Nevertheless, on 
weighing the probabilities of the case, we think it nearer the truth to 
speak of excitation by thermic injury rather than of thermic excitation 
proper, and we incline to the opinion that moderate heat in plants as 
well as in animals is anti-excitatory. 
Note by Dr. Waller.—We find it difficult at the present stage to 
reconcile this conclusion with the undoubted fact that up to a certain 
limit the rate of chemical change is augmented by rise of temperature. 
It might have been anticipated a priori that sudden rise of temperature 
would arouse greater chemical action of the same character as that 
aroused by mechanical or electrical excitation, and therefore an electrical 
change of the same sign. As a matter of fact, however, the electrical 
change aroused by moderate heat, as stated above, has always proved to 
be of the opposite sign to that aroused by mechanical and by electrical 
excitation. 
Note by Dr. V. H. Veley.—Dr. Waller has referred to me the 
difficulty set forth in the preceding note. The answer, as far as I am 
able to judge from the data, can be given as follows :— 
Limiting our attention to muscle only, let us suppose a potential 
(and partial) chemical change, which becomes actual under slight varia- 
tions of conditions, of a certain nature-stuff, called hereafter, for the 
sake of brevity, ‘inogen.’ Let us further suppose that this chemical 
change can take place in either of two directions, namely those of com- 
bination and of dissociation, being a simple reversible change of the type 
X+Y 2 XY. Let us assume that such change is endothermal at a 
: Brecht, ‘Observations on the Nature of Heat-Paralysis in Nervous. Tissues.’ 
American Journal of Physiology, vol. xxii., September 1, 1908. : 
