324 



ESTIMATION OF HEAT. 



(3) If the position of an organ be such, or if other conditions cause it to give 

 off heat by conduction or radiation, then its temperature falls. 



A good example of this is the skin, which varies greatly in temperature according to the 

 temj>erature of the surrounding medium, whether it is covered or uncovered, whether it is dry 

 or moist with sweat (which abstracts heat when it evaporates). When much cold food or drink 

 is taken, the stomach is cooled, and when ice-cold air is breathed, the respiratory passages 

 as far as the bronchi are cooled. 



211. ESTIMATION OF HEAT. Calorimetry is the method of determining 

 the amount of heat possessed by any body, or what amount of heat it is capable of 

 producing. The unit of measurement is the "heat-unit," i.e., the amount of heat 

 (or potential energy) required to raise the temperature of 1 gramme of water 1 C. 

 (see Introduction). 



Experiment has shown that equal quantities of different substances require very unequal 

 amounts of heat to raise them to the same temperature, e.g., 1 kilo, water requires nine times as 

 much heat as 1 kilo, iron to raise it to the same temperature. In the human body, therefore, 

 which is composed of very different substances, unequal amounts of heat will be required to 

 raise them all to the same temperature. The same amount of heat transferred to two different 

 substances will raise them to different temperatures. Hence, bodies of different temperatures 

 may contain equal amounts of heat. The amount of heat required to raise a definite quantity 

 (e.g., 1 grin.) of a substance to a certain higher degree (e.g., 1 C.) is called " specific heat. " 

 The specific heat of water (which of all bodies has the highest specific heat) is taken as = l. 

 By "heat-capacity" is meant, that property of bodies in virtue of which they must absorb a 

 given amount of heat in order to have a certain temperature. 



Calorimetry is employed : I. To determine the specific heat of the different organs 

 of t/ie body. Only a few observations have been made. The mean specific heat 

 of the following animal parts (water = 1) is : 



1-02 (?) Human muscle = 0741 

 1-031 (?) Ox muscle = 0787 



0-892 (?) Compact bone = 0"3 

 0-992 Spongy bone = 071 



The specific heat of the human body, as a whole, is about that of an equal volume 

 of water (]). 



Kopp's Method. The solid to be investigated is broken in pieces about the size of a pea, and 

 placed in a test-tube, A, with thin walls, which is closed above with a cork, from which a 



copper wire with a hook on it projects (fig. 

 231). The test-tube contains a certain 

 quantity of fluid which does not dissolve 

 the substance, but which lies between its 

 pieces and covers it. It is weighed three 

 times to ascertain the weight (1) of the 

 empty glass, (2) after it is filled with the 

 solid substance, (3) after the fluid is added, 

 so that we obtain the weight of the solid 

 substance, m, and that of the fluid, /. 

 The test-tube and its contents are placed 

 in a mercury bath, BB, and this again in 

 an oil bath, CC, and the whole is raised 

 to a high temperature. Into BB there is 

 introduced a fine thermometer, T. When 

 the tube, A, has reached the necessary tem- 

 perature (say 40) it is rapidly placed in 

 the water of the accompanying calori- 

 meter-box, DD. The water in this box, 

 which also contains a thermometer, D, is 

 kept in motion until it has completely 

 absorbed all the heat given off by A. Let 

 1^ represent the temperature to which A and its contents were raised in the mercury bath, and 



Human blood = 



Arterial blood = 



Venous blood = 



Cow's milk = 



Fat tissue - 0712 



Striped muscle 0;825 



Defibrinated blood = 0*927 



(J. Rosenthal.) 



Fig. 231. 

 Kopp's apparatus for estimating specific heat. 



T, the temperature to which it fell in the calorimeter; let s be the specific heat, and m the 

 weight of the solid substance in the test-tube, while <r and M represent the specific heat of the 

 weight of the interstitial fluid in the test-tube ; and lastly, let w equal the amount of water in 

 contact with A, which absorbs and gives off heat ; then W represents the amount of heat 

 which the test-tube and its contents give off during cooling 



