Heat by Conduction in Bone, Brain-tissue, and Skin. 189 



Comparing the above table with Table II, we find that the average 

 difference in the conducting powers of skull and brain-tissue is now 

 reduced to o, 00971 C, in favour of the bone; but if we take the 

 maximum values, the conductivity of brain-tissue slightly exceeds that 

 of skull, namely, by 0° '00038 C. 



Experiments on Shin. 



The skin experimented on was fresh sheep's skin; and, in the par- 

 ticular experiments with which we have now to deal, pieces of the 

 shaven scalp 3 millims. in thickness, and of the same area as the 

 pieces of skull and cerebrum already described, were employed. 



Following the course adopted with skull and brain-tissue, we have 

 the same points as before to consider. 



(a.) The time required for the first sign of the change of tempera- 

 ture to show itself through the piece of scalp. 



The average degree of difference of temperature to which the scalp 

 was subjected w^as 0°*12957 C, the maximum and the minimum being, 

 respectively, 0°*1645 C. and 0°*125 C. With these differences the 

 time required for the first sign of the change of temperature to 

 manifest itself, on the upper surface of the piece of skin — with the 

 apparatus set, as before, to detect 0°*0006742 C. — was 17*6 seconds. In 

 60 per cent, of the cases the time was 19 seconds ; while the other 

 40 per cent, was divided equally among 23, 16, 15, and 8 seconds. 



Reducing all the results to values representing o, l C. difference of 

 temperature, the average time is found to be 22*88 seconds, the 

 extremes being 29*417 and 10 seconds. The average rate of the 

 thermal movement is consequently 1 millim. per 7' 6267 seconds, the 

 maximum and the minimum times being, respectively, 9*8057 and 

 3*3333 seconds. The average rate of the thermal transmission per 

 millimetre for 0°*1 C. difference of temperature appears, therefore, to 

 be lower, afc this period, in scalp than in bone or brain-tissue ; and the 

 lowest rate in scalp is below the corresponding rates in bone and 

 brain-tissue ; but on the other hand, the highest rate is found in scalp, 

 although the degree of superiority is insignificant. In Table V the 

 results obtained on the three tissues, at this period, are brought 

 together for comparison. 



(6.) The degree of change of temperature produced at certain 

 measured intervals of time. 



