436 THERMAL CONDUCTIVITY OF THE TISSUES. 



II. Calorimetry is more important for determining the ammint of 

 heat produced in a given time by the body as a whole, or by its in- 

 dividual parts. 



Lavoisier and Laplace made the first calorimetric observations on animals in 

 1783, by means of an ice-calorimeter; a guinea-pig melted 13 ozs. of ice in 10 

 hours. Crawford, and afterwards Dulong and Despretz (1824), used Rumford's 

 water-calorimeter, which is similar to the one already described viz., of Favre 

 and Silbermann. Small animals are placed in the inner thin-walled copper 

 chamber (K), which is placed in a water-bath surrounded on all sides by some 

 non-conducting material. We require to know the amount of water, and its 

 original temperature. The number of calories is obtained from the increase of the 

 temperature at the end of the experiment, which lasts several hours. The air is 

 supplied to the animal through a special apparatus resembling a gasometer. The 

 amount of GQ 2 in the gases evolved is estimated chemically. 



According to Despretz, a bitch forms 14,610 heat-units per hour 

 i.e., 393,000 in 24 hours. Other things being equal, a man seven 

 times heavier than this would produce in 24 hours about 2,750,000 

 calories. Senator found that a dog weighing 6,330 grms. produced 

 15,370 calories, and excreted at the same time 3,67 grms. C(X. The 

 first calorimetric experiments on man were made by Scharling (1849). 

 Liebermeister estimated the amount of heat given off by a man placed 

 in a cold bath, which was surrounded with a woollen covering. Leyden 

 placed a lower limb in the calorimeter, whereby 6,000 grms. water were 

 raised 1C. in an hour. If we assume that the total superficial area 

 of the body is fifteen times greater than that of the leg, the human 

 body would produce 2,376,000 calories in 24 hours. 



212. Thermal Conductivity of Animal Tissues. 



The thermal conductivity of animal tissues is of special interest in connection 

 with the skin and subcutaneous fatty tissue. The fatty layer under the skin, 

 more especially in the whale, walrus, and seal, forms a protective covering, 

 whereby the conduction of heat from internal organs is rendered almost impos- 

 sible. Investigations upon this subject, however, are few. Griess (1870) 

 attempted to estimate the thermal conductivity by heating one part of the tissue, 

 and determining when and in what direction pieces of wax placed on the tissue to 

 be investigated began to melt. He investigated the stomach of the sheep, the 

 bladder, skin, hoof, horn, and bones of an ox, deer's horn, ivory, mother-of-pearl, 

 shell of haliotis. He found that fibrous tissues conducted heat more readily in 

 the direction of their fibres than at right angles to the course of the fibres. 

 Hence, the figures obtained from the melted wax were usually elliptical. Landois 

 has made similar observations, and he finds that tissues conduct better in the 

 direction of their fibres. After bones, blood-clot was the best conductor, then 

 followed spleen, liver, cartilage, tendon, muscle, elastic tissue, nail and hair, 

 bloodless skin, gastric mucous membrane, washed fibrin. It is specially interest- 

 ing to note how much better skin containing blood in its blood-vessels conducts 

 compared with bloodless skin. Hence little heat is given off from a bloodless 

 skin, while congested skin conducts and gives off much more heat. 



