Heat by Conduction in Bone; Brain-tissue, and Skin. 103 



Placing the above beside Tables II and IV, even leaving ont the 

 question of relative thickness, the inferior conducting power of skin, 

 compared with bone and cerebral tissue, is again manifest, although 

 the degree of this inferiority is diminished. Thus, taking the 

 averages at the end of the sixth minute, the skin falls below bone by 

 24*08 per cent., and below brain-tissue by 12 347 per cent. ; while now 

 these differences are reduced, respectively, to 18*404 per cent., and 

 8*694 per cent. If we take the maximum values, the skin is inferior 

 to bone (the maximum value of the latter being a trifle lower than that 

 of brain-tissue) by 20*229 per cent, at the end of the sixth minute, and 

 by 14*06 per cent, in the permanent thermal condition. With regard 

 to the minimum values, they are now, as at former periods, higher in 

 skin than in brain-tissue. 



Conduction in Bone and Shin combined. 



Let us now suppose the 3 millims. of scalp to be lying upon 

 the 7*5 millims. of bone, as in life, and a rise of temperature of 0°*1 C. 

 to occur on the cerebral surface beneath. We have seen that the 

 dura mater offers no appreciable resistance, and have, therefore, 

 simply to deal with the compound conductor of bone and skin. We 

 will first estimate how long a time would elapse after the rise of tem- 

 perature in the brain before 0°*0006742 C. difference would be found 

 on the outer surface. Xow it has been shown that the average time 

 required for *1 C. to traverse the bone is 37*3 seconds, while the 

 average time required for the same difference of temperature to tra- 

 verse the skin is 22*88 seconds ; the total time would therefore, be 

 60*18 seconds, the shortest time would be 36*39 seconds, and the 

 longest time 85*277 seconds. 



Next, with regard to the amount of heat which would be trans- 

 mitted through the compound conductor. Looking at Table I we see 

 that the bone has transmitted, at the end of 1 minute 15 seconds, 

 ] 6*09 per cent, of the heat received, and from Table VI we learn that, 

 during the same time the skin has transmitted 11*597 per cent. ;* 

 therefore, the skin receiving from the bone 16*09 per cent, of the 

 original amount of heat would transmit 11*597 per cent, of these 

 receipts, or 1*86395 per cent, of the original amount; hence the 

 change of temperature observed on the outer surface of the scalp, at 

 this period, would be 0°*001^'36 C. Table VIII gives the results, 

 for the several periods of time, deduced in the above manner from 

 Tables I and VI. These results show that, in spite of the decided 

 resistance introduced by the skin, there would not be the slightest 

 difficulty in detecting, with delicate apparatus, at an early period, on 



vol. xxxiv. 



* Averages. 



O 



