192 



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



If we should apply the well-known physical calculations of Fourier 

 and others, and through them seek to determine the changes of tem- 

 perature which would exist if the piece of skin were increased in 

 thickness to 7*5 millims., the inferiority of the tissue in conducting 

 power compared with bone and brain-tissue, would become much more 

 striking ;* but unfortunately, not only theory — based upon the lack of 

 homogeneity in these structures — but also a large number of direct 

 experiments made by the writer, show that such calculations are not to 

 be relied upon. In the case alone of the hard tissue of bone, it has 

 sometimes happened that the results of the mathematical calculations 

 and those of the experiment have partially agreed. We cannot, then, 

 with any certainty, reason from one thickness of bone, brain, or skin 

 to another. To have reduced the bone to .3 millims. in thickness to 

 correspond with the skin, would have entailed serious risks of error in 

 the method of experimenting adopted. f The thickness of bone chosen 

 was a natural thickness of the skull often found in the animal experi- 

 mented on, and the same is true of the thickness of the scalp. 



(c.) The maximum change of temperature produced, when the 

 permanent thermal condition is attained. 



With the differences of temperature given under the heading (a), 

 the permanent thermal condition was reached in a time ranging from 

 11 to 15 minutes, the average being 12 minutes 15 seconds. In 50 

 per cent, of the cases the time was 11 minutes, and the other 50 per 

 cent, was divided equally between 12 and 15 minutes. 



In Table VII we see the effects of the thermal movement at this 

 stage, reduced as before to the basis of 0°'l C. difference of tempera- 

 ture. 



Table VII. — Permanent thermal condition effected by o, l C. through 

 3 millims. of sheep's scalp. 1° of galvanometer is equal to 

 0°-0006742 0.; and 0°*1 C. is equal to 148°-316 of galvonometer. 





Degrees of 



Thermornetric 



Percentages of 





galvanometer. 



values. 



heat transmitted. 



Averages 



100-155° 



0-06751° C. 



67*514 per cent. 





117 480 



0-07920 



79-209 





82-104 



005535 



55-354 



* The application of these formulae sweeps away the whole of Table VI, as 

 according to them, even at the end of the sixth minute no sign of the transmission 

 would be found through 7'5 millims. of scalp. 



f By exchanges between the face of the pile and the water through the paraffine 

 envelope (see note, p. 181), which latter would, with the above thickness of bone, 

 be in dangerous proximity to the liquid. 



