INTRODUCTION 



obtained, and we can be certain that any matter found in the body must 

 have been derived from without. There is no creation or destruction of 

 matter in the body. 



The determination of the equation in the case of the total energy of the 

 body is rather more difficult. We have, in the first place, to measure the 

 total income and output of the body, and to determine the total heat which 

 would be evolved by the oxidation of tb ?. foodstuffs taken into the carbon 

 dioxide, water, &c., that are given out. We must then compare the figure 

 so obtained with the actual output of energy by the body. The latter can 

 be measured in terms of heat by placing the animal inside a calorimeter. 

 Many practical difficulties arise in the performance of the experiment, in 

 consequence of the necessity of providing the animal with a constant supply 

 of air to breathe, and of allowing for the continual loss of water by evapora- 

 tion which is going on at the surface of the animal. The first accurate 

 experiments of this nature were made by Rubner. This observer deter- 

 mined by means of the calorimeter the total heat loss of dogs. In the same 

 animals the material income and output of the body were measured, and a 

 calculation was made as to the amount of energy which would be set free 

 in the body by the processes of oxidation involved in the change of material 

 observed. The following Table represents a summary of Rubner's results : 



It will be seen that the average difference between the calculated and 

 observed results amounts only to I'Ol per cent. an amazing agreement 

 considering the extreme difficulties of the experimental methods involved. 

 The important deduction to be drawn from these observations is that the 

 foodstuffs which are oxidised in the body develop in this process exactly 

 the same amount of energy as when they are burnt up outside the body. 



From one aspect, therefore, the animal body may be looked upon as a 

 machine for the transformation of the potential energy of the foodstuffs 

 into kinetic energy, represented by the warmth and movements of the body 

 as well as by other physical changes involved in vital processes. In the living 

 organism we cannot, however, distinguish between the source of energy and 

 the machinery, as we can in the case of our engines. When we endeavour 

 to trace the foodstuffs after their entry into the body, we lose sight of 



