18 6 Dr. J. S. Lombard. On the Propagation of 



Table II. — Permanent thermal condition effected by 0°'l C. through 7*5 

 millims. of sheep's skull. 1° of galvanometer is equal to 0°'0006742 C, 

 and o- l C. is equal to 148°\316 of galvanometer. 





Degrees of 

 galvanometer. 



Tkermometric 

 values. 



Percentages of 

 heat transmitted. 



127 431° 

 138 333 

 104-800 • 



0-08591° C. 



0-09326 



007065 



85-918 per cent. 



93-269 



70659 



We find from the above table that in the permanent thermal state — 

 reached in the majority of cases, as we have just seen, by the tenth 

 minute — the initial difference of temperature of 0°'l C. between the 

 two surfaces of the bone is, on the average, reduced to 0°'01409 C, 

 nearly 86 per cent, of the excess of heat on the warmer of the two 

 surfaces being now transmitted to the cooler surface. 



Experiments on Brain-Tissue. 



The brain-tissue used was that of the sheep, and was in a fresh 

 condition. Pretty much the whole of the brain was examined, and 

 blocks of different thicknesses and areas were employed, but the expe- 

 riments with which we are at present concerned were made on pieces 

 cut from the upper surface of the cerebrum, 7'5 millims. in thickness 

 and of an area of 21'5 millims. by 15 millims., being thus identical in 

 dimensions with the pieces of skull already treated of. A preliminary 

 series of experiments had, however, to be made to determine whether 

 the dura mater opposed any noteworthy barrier to thermal transmis- 

 sion. This question was decided in the negative, it being found that 

 the resistance of the membrane in question was so slight that it could 

 safely be disregarded. 



We will examine the results obtained on the pieces of brain in the 

 same manner as was adopted in the case of the skull. 



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

 ture to show itself through the piece of brain. 



The average degree of difference of temperature to which the brain- 

 tissue was subjected was 0°'13116 C, the maximum being o, 1513 C. 

 and the minimum being o, 1202 C. With these differences, the 

 average time elapsing before the first appearance on the upper surface 

 of the piece of tissue of the thermal change (the apparatus having the 

 same delicacy as in the experiments on the skull) was 30"88 seconds. 

 In 44*441 per cent, of the cases it was 23 seconds, in 27'777 per cent. 



