CALORIMETRY. 325 



W = (s.m + w + a ft) (T-TJ . 

 The amount of heat, W lf absorbed by the calorimeter is 



Wj-M (<!-*), 

 where M represents the amount of water in the calorimeter, t the original temperature of the 

 water in the calorimeter, and t x the temperature to which it is raised by placing A in it. If 

 W and Wj are equal, then 



tke specif Mat, ^(^W^XT-T,) ^ 



If a fluid substance is placed in the test-tube, and its weight = m, and its specific heat = s, 

 the formula for the specific heat of the fluid to be investigated is 



Mfo-Q-totT-T! ) 



II. Calorimetry is more important for determining the amount of heat produced 

 in a given time by the body as a whole, or by its individual parts. 



Lavoisier and Laplace made the first calorimetric observations on animals in 1783, by means 

 of an ice-calorimeter ; a guinea-pig melted 13 oz. of ice in ten hours. Crawford, and afterwards 

 Dulong and Despretz, used Rumford's water-calorimeter, which is similar to Favre and 

 Silbermann's. 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 C0 2 in the gases evolved is estimated. 



According to Despretz, a bitch forms 14,610 heat-units per hour i.e., 393,000 

 in twenty-four hours. Other things being equal, a man seven times heavier than 

 this would produce in twenty-four hours about 2,750,000 calories. Senator found 

 that a dog weighing 6330 grms. produced 15,370 calories, and excreted at the same 

 time 367 grms. C0 2 . 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 6000 grms. water were raised 1 

 C. 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 twenty-four hours. 



212. THEEMAL CONDUCTIVITY OF 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 impossible. 

 Investigations upon this subject, however, are few. Griess 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 interesting to note how much better skin containing blood in its blood-vessels 

 conducts than does bloodless skin. Hence little heat is giyen off from a bloodless skin, while 

 congested skin conducts and gives off much more heat. 



Like all other substances, the human body is enlarged by heat. A man weighing 60 kilos., 

 and whose temperature is raised from 37 C. to 40 C, is enlarged about 62 cubic centimetres. 

 Connective-tissue (tendon) is extended by heat, while elastic tissue and the skin, like caoutchouc, 

 are contracted. 



213. VARIATIONS OF THE MEAN TEMPERATURE. (1) General 

 Climatic and Somatic Influences. In the tropics the mean temperature of the 

 body is about V C. higher than in temperate climates, where again it is several 

 tenths of a degree warmer than in cold climates ; but this has recently been 



