Heat by Conduction in Bone, Brain-tissue^ and Skin. 177 



3 inillims. asunder. This close proximity of the two junctions must 

 have very greatly diminished the delicacy of the arrangement, as a 

 change of temperature at one junction would speedily be propagated 

 to the other, setting up a reverse current in the latter.* Moreover, 

 considering how good a conductor the brain-tissue is, a slight change 

 of temperature in the point of brain in contact with one junction 

 would very quickly be felt in the point in contact with the other 

 junction, only 4 or 5 millims. of tissue intervening. Again, the 

 galvanometer appears to have been less sensitive in these experiments 

 than in those first cited. Yet M. Schiff obtained deflections of 12° to 

 14° from the insignificant psychical processes aw r akened in these 

 animals by the exhibition of coloured papers, &c. It is very evident 

 that, under such adverse circumstances as those specified, the absolute 

 rise of temperature must have been considerable to have given any 

 sort of a balance to one point over the other. 



Weighing all the evidence, then, there does not appear to the 

 writer, to be the slightest reason why rises of temperature as high as 

 o, 3 C. should not occur in the brain of man during mental activity ; 

 and elevations of o, 2 C. are certainly admissible ; but the results 

 which will be given in this paper are based on values of only 0°'l C. 



In the present experiments, instead of making use of differences 

 of temperature of 1° C, or more, fractions of a degree have been em- 

 ployed, as furnishing more conclusive proof of the possibility of the 

 transmission of small differences of temperature, than could be 

 afforded by the mere reasoning from larger to smaller values. We 

 will consider first the apparatus employed, and then the methods of 

 experimenting. 



Apparatus Employed. 



The instruments employed in testing the conductivity of the tissues 

 under consideration, were as follows : — 



First. — Thermo-electric piles of from one to four pairs, composed of 

 the antimony-zinc-cadmium alloy of Professor Moses G. Farmer, 

 joined to bismuth as the other metal. The general construction of 

 these piles has been fully described elsewhere, f and the only point of 

 difference to which special attention need be called here, is, that 

 whereas, in the description referred to, the conducting wires are 

 represented as composed of copper strands, in the present instance they 

 consisted of single fine copper wires 0*011 inch in diameter, — con- 



* See the writer's remarks on reverse currents in piles, in " Regional Temperature 

 of the Head," p. 6. It would have been almost utterly impossible to have tested 

 the thermometric values of a pile so constructed, — at least such is the writer's 

 experience. 



f See the writer's work " Regional Temperature of the Head," p. 19. The par- 

 ticular alloy referred to above is the one designated " No. 1." 



VOL. XXXIV. N 



