BY DR. BURDON-SANDERSON. 337 



SECTION I. CALORIMETBT. 



The production of heat is one of the essential functions of 

 living tissue ; consequently, wherever there are living cells, 

 heat is generated at all times. We assume, at the outset, that 

 the source of production is the sum of the chemical processes 

 which take place in the body ; and that under all circum- 

 stances, so long as the tissues are neither growing nor wasting, 

 the quantity of heat produced by the oxidation of the food 

 consumed is equal to the quantity which would have been 

 produced had the same quantity of oxidizable substance been 

 converted into similar more or less oxidized products out of 

 the body. 



115- There are two distinct methods by which a theoretically 

 complete determination of the quantity of heat products in 

 the body in a given time can be arrived at. The first consists 

 in deducting the heat-producing power (heat value) of the 

 substances discharged from the body in a given time, from the 

 heat value of the substances consumed. The second is based 

 on the actual measurement of the quantity of heat discharged 

 in a given time. In the former case the difference obtained 

 expresses the amount of heat produced in the period, provided 

 that the animal is in a state of nutritive equilibrium i. e., 

 that its tissues are neither growing nor wasting. In the latter, 

 the measurement gives the desired result, provided that the 

 discharge is exactly equal to the production of heat i. e., that 

 the temperature of the body remains the same. 



With reference to the first method, as it reposes entirely on 

 chemical and physical operations, some of which do not fall 

 within the scope of this work, while others will be described 

 under other heads, all that is necessary is to make clear the 

 principles of its application. So long as an animal is in 

 nutritive equilibrium (see above) the combustible material 

 actually consumed, i. e., oxidized in its body in a given time, 

 may be known by deducting, from the quantity of such 

 material actually swallowed, the quantity discharged in the 

 faeces. This determination is, therefore, purely a question of 

 chemical analysis. 



The heat-producing powers of the chief constituents of food 

 have been determined approximatively by Frankland, who 

 finds, for example, that one gramme of albumin, in under- 

 going complete combustion into water, carbonic acid, and 

 ammonia, produces heat enough to raise 4998 grammes of 

 water one degree centigrade. This fact we express by stating 

 that 4998 is the heat value of albumen. In like manner 

 Frankland has found the heat value of lean beef to be 5103, 

 and of the fat 9069. If, therefore, it were possible to 

 determine how much of any of these substances is consumed, 

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