Heat by Conduction in Bone, Brain-tissue, and Skin. 181 



out in the centre of the mass, extending from the upper surface to the 

 pasteboard bottom ; at and near this latter point the area of the space 

 was just large enough to accommodate the piece of tissue to be tested. 

 The pasteboard bottom under the space was next cut out, and its 

 place supplied by a copper plate less than 0*5 millim. in thickness, 

 which was closely and exactly fitted in, melted paraffine being used on 

 the inside to secure it. The substance to be tested, when in position, 

 therefore rested on the thin copper plate, and was surrounded by 

 paraffine walls.* The pile (enveloped at the end near its face in only 

 a thin layer of paraffine-soaked wool, so as not to touch the surrounding 

 walls of paraffine) was pressed down firmly upon the substance lying on 

 the copper plate, and was kept in position by wedging with cotton- 

 wool the space between its envelope, near the upper end of the latter, 

 and the paraffine walls. The reason for preventing the envelope of the 

 pile near its face from touching the surrounding paraffine walls, is that 

 the latter are, at the bottom of the box, in almost direct contact with 

 the water ; and as paraffine conducts about as well as the substances 

 tested, a thermal movement might possibly take place directly, between 

 the face of the pile and the water, through the paraffine walls. The 

 intervention of an air-space between the envelopes of the pile and the 

 paraffine wall, not only in the neighbourhood of the face of the pile, 

 but extending to a point far beyond the entire length of the latter, 

 rendered any such thermal movement impossible. Two strips of 

 pasteboard were fitted to the sides of the box, in the same way as 

 in the case of bone. These strips, moreover, served as supports for a 

 mass of cotton- wool, which covered the top of the box, in order to cut 

 off communication between the air imprisoned in the box and the ex- 

 ternal atmosphere through any chance crevice in the cotton-wool 

 wedges holding the pile in place. 



The prepared bone, or the paraffine box containing the piece of brain 

 or skin, having been attached to the claw of the sliding arm mentioned 

 on page 180, by means of the pasteboard strips, is brought over the 

 surface of the water, and then carefully lowered until the under 

 surface of the bone or the copper plate in the bottom of the box is 

 just immersed, and no more, in the liquid. f When this is effected the 

 sliding arm is made fast, and the bone or box removed by raising the 

 whole arrangement, as one piece, by means of the perpendicular rod 



* In comparing bone with, brain and skin, it was found that the interposition of 

 the copper plate had no effect on either the rapidity or the extent of the thermal 

 transmission. This was proved by covering the under surface of a piece of bone, 

 previously tested, with a copper plate of the thickness of that used in the experi- 

 ments on brain and skin, when it was fouud that the conductivity remained un- 

 changed. 



f The necessity of the caution contained in the note at the bottom of page 180 

 will now be obvious. 



