INTRODUCTION. 7 



importance of the science from the theoretical standpoint as 

 well as in its practical relations to medicine. 



It remains to briefly mention the development of another 

 field of scientific study because of its bearing on certain prob- 

 lems of physiological chemistry. In the last quarter of the 

 eighteenth century Lavoisier clearly showed the nature of 

 combustion and the relation of animal heat to respiration and 

 the oxidation of the tissues. Lavoisier and Laplace carried 

 out the first quantitative experiments in which a calorimeter 

 was employed to measure the evolution of body heat. These 

 were repeated by Despretz in 1824 and later by Dulong. 

 Since then by greatly improved methods many similar inves- 

 tigations have been made. 



A little later than the date on which Lavoisier and Laplace 

 announced their important researches on the relation of animal 

 heat to oxidation of foodstuffs, Benjamin Thompson, Count 

 Rumford, announced a discovery of equally far-reaching con- 

 sequences. He made the observation that the heat of friction 

 between two pieces of metal may be absorbed by water and 

 so measured, and that there is a relation between the mechan- 

 ical work lost in the friction and the heat generated. He 

 made also the curious observation that the work performed by 

 the horse in one of his experiments in which friction was pro- 

 duced depended in turn on the combustion or oxidation of the 

 food of the horse, from which it followed that indirectly the 

 heating of the water was due to the combustion of a certain 

 amount of food. But all the consequences of his experiments 

 Rumford did not see. He was mainly interested in showing 

 the absurdity of the notion of the material nature of heat, then 

 commonly held, which he did completely. It remained for 

 Joule of England and Mayer of Germany to point out, nearly 

 fifty years later, the true relation between heat and work. In 

 fine by establishing the work equivalent of heat they made it 

 possible to calculate the food equivalent of work, since the 

 food equivalent of heat had been already proven. These rela- 

 tions are all of the highest value in the study of metabolism, 

 to be considered in the sequel. 



