482 



PHYSIOLOGICAL PHYSICS. [Chap, xxxix. 



For example, while 1 grin, of egg albumen fully 

 oxidised yields 4,998 heat units, the same quantity 

 oxidised to urea yields 4,263 heat units, that is, 735 

 units less ; and 1 grm. ox flesh completely oxidised 

 yields 5,103, l>ut only 4,368 if oxidised to urea. 



The quantity of heat capable of being yielded up 

 by the food on complete oxidation must, therefore, be 

 reduced by the amount which the excreta will pro- 

 duce. 



During bodily repose, the energy due to chemical 

 combination all' appears as heat. If work be done, 

 heat disappears to the extent of the equivalent of the 

 work done. About one-fifth of the total energy of 

 the human body appears as mechanical work, and 

 four-fifths are expended as heat. 



Apart from chemical actions, there are physical 

 causes at work in the production of heat, the friction 

 of parts, for example, of which, however, it is impos- 

 sible to render an account. 



The amount of heat liberated by the animal 



body in a given time has 

 been estimated by various 

 experiments by means of 

 the calorimeter. The 

 apparatus of Dulong is 

 shown in Fig. 197. It 

 consists of a chamber c 

 into which the animal to 

 be experimented on is 



P laced " chamber is 





Fig. 197.-Calorimeter of Dulong. 



immersed in the calori- 



meter w, made of metal with a bright outer surface 

 and japanned inside, which is itself contained in a 

 much larger wooden case, so that a space M exists be- 

 tween the calorimeter and outer case. The space is 

 stuffed with tow or some such non-conducting material. 

 The case is also higher than the calorimeter, and is 



