284 Biology in America 



by the combustion of the carbon in the body, or its union 

 with oxvf^en to j)ro(luee carbon dioxide. In support of this 

 assumption he pointed out that in birds, whose temperature 

 is higher than that of mammals, there is a greater production 

 of carbon dioxide in respiration. 



To test tliis hypothesis Lavoisier constructed a primitive 

 calorimeter for measuring the heat production of the animal 

 body. This consisted essentially of two chambers, an inner, 

 for holding the animal whose heat production was to be 

 measured, and ^n outer of double walls, the space between 

 which, as well as that of the outer chamber itself, was packed 

 with ice. Knowing the amount of heat required to melt a 

 given quantity of ice, and measuring the carbon dioxide and 

 water produced by the animal, it should be possible to deter- 

 mine whether the respiration of the animal was of the proper 

 amount to account for the heat produced. Without going into 

 details regarding these experiments of Lavoisier, and his suc- 

 cessors Dulong and Depretz, it is sufficient to say that the 

 results of these early experimenters showed a very close 

 correspondence between the heat calculated from the respira- 

 tory products formed, and the actual production of heat in 

 the calorimeter and led to the conclusion established by later 

 observers that the production of energy in the animal body 

 is dependent on the oxidation of the food consumed, and 

 further that conservation of energy is just as true of the 

 latter as of any non-living machine. 



The work of these early experimenters has been continued 

 in recent years by Benedict and Atwater at the Nutrition 

 Laboratory of the Carnegie Institution in a series of brilliant 

 investigations with the aid of a very ingenious and intricate 

 respiration calorimeter. This in brief consists of a chamber 

 large enough for a man to live in for several days at a time, 

 and containing apparatus (i. e., a bicycle) on which exercise 

 may be taken. The chamber is constructed of a double metal 

 wall with a contained air space and is surrounded with a 

 double wall of wood containing a second air space, while 

 between metal and wooden walls is an intermediate air space, 

 the whole very effectively preventing any exchange of heat 

 between the interior and exterior of the chamber. As a fur- 

 ther precaution to prevent such exchange of heat special 

 electrical devices are installed for keeping the two walls of the 

 metal chamber at the same temperature, and any difference 

 in temperature between them is recorded on a galvanometer 

 on the observer's desk in the laboratory. Connected with 

 the chamber are various devices for measuring the intake of 

 oxygen, the outgo of carbon dioxide and water, the heat lost 

 by the subject during the experiment and the amount of 



