Heat by Conduction in Bone, Brain-tissue, and Skin. 197 



Table XI. — Permanent thermal condition effected through 7'5 millims. 

 of sheep's skull and 3 millims. of sheep's scalp, taken together, 

 lying over a point of cerebral surface 7"5 millims. distant from 

 another point of this same surface, the temperature of which latter 

 point is raised o, l C. The results are calculated from Tables IV 

 and IX. This Table is for comparison with Table IX, where the 

 effects of the direct transmission from the heated point are given. 

 1° of galvanometer is equal to o, 0006742 C. ; and 0°'l C. is equal to 

 148° *316 of galvanometer. 





Degrees of 

 galvanometer. 



Thermometric 

 values. 



Percentages of 

 heat transmitted. 



65-563° 

 102-606 

 28-160 



0-044202° C. 



0-070176 



0-018985 



44*202 per cent. 



70176 



18-985 









Plainly, if it were a question of mere conduction alone, and if the 

 skull and skin at the several points were of equal thickness, and 

 possessed of the same conductivity, it would be easy to locate on 

 the outer surface, within a radius of 7*5 millims., a change of o, l G. 

 occurring on the cerebral surface. 



The following are the differences of temperature in favour of the 

 point of surface lying directly over the focus of heat, which would 

 be found under the circumstances we are considering : — 



Times. 



Average differences 

 of temperature. 



Permanent thermal condition. 





Differences of 

 temperature. 



1 min. 15 sec . . 



2 „ „ ... 

 4 „ „ ... 

 6 „ ... 



0-001602° C. 

 0-004406 

 0011842 

 0-014202 



0-013804° C. 



0-003701 



0-020127 



But, in truth, in the case of the tissues concerned, we are not, in the 

 first place, dealing with simple homogeneous conductors of uniform 

 thicknesses. Even within the narrow area specified, the bone or skin 

 may exhibit decided differences of conductivity, due to slight varia- 

 tions of structure or composition. That this may be the case, the 

 writer has over and over again proved by direct experiment. As the 



* It will be noticed that the least difference is found with the maximum of trans- 

 mission, and the greatest difference with the minimum of transmission. 



