Heat by Conduction in Bone, Brain-tissue, and Skin. 183 



minute according to the rate of movement of the index of the galva- 

 nometer, which was usually much diminished by this time, the per- 

 manent thermal condition, or state of thermal equilibrium, being now, 

 as a rule, not very far off. The readings of the thermometers and of the 

 thermo-electric apparatus used in testing the differences of tempera- 

 ture between the air and the water, were noted every half minute. 

 As it was not the rule — even when the greatest care was used — to find 

 the index of the galvanometer at 0° of the scale at the start, it was 

 almost always necessary to add to or subtract from the readings of the 

 thermometers the thermometrical value of the deflection at the moment 

 when the instrument began to show the first sign of the thermal trans- 

 mission. Thus, suppose the thermometers to show a difference 

 between the air and the water of o, 125 C. in favour of the former, 

 and the index of the galvanometer to be 5° of its scale on the cold 

 side of 0°. If the galvanometer be set to show 1° deflection as equal to 

 0°'0006742 C, we must deduct 0°-003371 C. (5x0-0006742) from the 

 o, 125 C. difference between the air and the water, since the surface 

 of bone or brain or skin in contact with the thermo-pile is already 

 cooler than the air by 0°'003371 C. The true thermometric difference 

 between the two surfaces of the substance under examination is, there- 

 fore, 0°-121629 C. 



Experiments on Bone. 



The bones examined were the skull and long bones of sheep, and 

 the ribs of oxen. 



In the experiments on the skull, pieces of various thicknesses and 

 areas were taken from different parts, but the results to be given here 

 were obtained with fresh pieces of the parietal and occipital bones 

 7*5 millims. in thickness, and 2T5 millims. by 15 millims. in area. 



We have three principal points for consideration, namely, as 

 follows : — 



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

 ture to show itself through the bone. 



(£>.) The degree of change of temperature produced at certain 

 measured intervals of time. 



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

 the permanent thermal condition is attained. 



Taking the above in the order in which they are set down, we have 

 first to consider the question indicated under the heading "a." 



To begin with, the degree of difference of temperature to which the 

 bone was subjected must be taken into account. The average degree 

 of difference of temperature was 0°"129 Q., the maximum being 

 o- 147 C, and the minimum o, 1136 C. Under these conditions, the 

 average time required for the first appearance through the bone of 

 the thermal change, with the apparatus set to detect o, 0006742 C, 



