INTRODUCTION 3 



Before we can make any accurate investigations of the conditions 

 which determine these activities, We must know whether the two great 

 laws of chemistry and physics, viz. the conservation of mass and the 

 conservation of energy, hold good for the processes within the living- 

 body. The many experiments which have been made on this point 

 have decided the question in the affirmative. Thousands of experi- 

 ments have been made, both on man and on animals, in which the 

 total income of the body, viz. food and oxygen, has been weighed, 

 and compared with the total output, viz. carbon dioxide, water, and 

 bodies allied to ammonia (urea, &c.). In every case complete equality 

 has been obtained, and we can be certain that any substance 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 the food- 

 stuffs taken in to the carbon dioxide, water, &c., that are given out. 

 We must then compare the figure so obtained with the actual outpi t 

 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 evaporation 

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

 experiments of this nature were made by Rubner. This observer 

 determined 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 : 



