84 PHYSIOLOGY FOR DENTAL STUDENTS. 



against the other, to a comparison of the smallest fragments into 

 which each can be broken. These are the elements and of them 

 carbon and nitrogen are the only ones which it is possible to 

 measure with accuracy in both intake and output. From bal- 

 ance sheets of intake and output of carbon and nitrogen and 

 from information obtained by observing the ratio between the 

 amounts of oxygen consumed by the animal and of carbonic acid 

 (C0 2 ) excreted, we can draw far-reaching conclusions regarding 

 the relative amounts of protein, fat and carbohydrate which have 

 been involved in the metabolism. As has already been stated, 

 the essential nature of the metabolic process in animals is one 

 of oxidation, that is to say, one by which large unstable mole- 

 cules are broken down to those that are simple and stable. Dur- 

 ing this process of katdbdism, as it is called, the potential energy 

 which is locked away in the large molecules becomes liberated 

 as actual or kinetic energy, that is to say, as movement and heat. 

 It therefore becomes of importance to compare the actual energy 

 which an animal expends in a given time with the energy which 

 has meanwhile been rendered available by metabolism. This is 

 called the energy balance. We shall first of all consider this and 

 then proceed to examine somewhat more in detail the material 



balance of the body. 







Energy Balance. 



The unit of energy is the large calorie (written C), which is 

 the amount of heat required to raise the temperature of one kilo- 

 gramme of water through one degree (Centigrade) of tempera- 

 ture. 1 We can determine the calorie value by allowing a meas- 

 ured quantity of a substance to burn in compressed oxygen in 

 a steel bomb which is placed in a known volume of water at a 

 certain temperature. Whenever combustion is completed, we 

 find out through how many degrees the temperature of the water 

 has become raised and multiply this by the volume of water in 

 litres. Measured in such a calorimeter, as this apparatus is 



iThe distinction between a calorie and a degree of temperature must be 

 clearly understood. The former expresses quantity of actual heat energy ; 

 the latter merely tells us the intensity at which the heat energy is being given 

 out. 



