150 THE HUMAN MOTOR 



In all the nervine aliments, two questions arise : 



1. Are they consumed in the organism producing a measur- 

 able amount of heat ? 



2. If not, what is their toxic dose, and what amount will 

 perform the functions of a digestive or neuro-muscular stimulant ? 

 These questions will be answered later. 



103. Alimentary Rations and Energetic Expenditure. From 

 analogy with other motors we deduce that the alimentation is 

 the source of the energy of the living motor. We are no longer 

 at the stage when a German doctor, Reech, could venture to 

 maintain the principle of " hereditary " animal heat. This 

 opinion elicited the following sally from Robert Mayer : "I 

 hope Reech will apply his principles and warm his room with a 

 stove whose heat was gathered formerly in an ancestral blast 

 furnace " (1843). 



Moreover, experimental demonstrations have verified the prin- 

 ciple of the conservation of energy in the animate matter. These 

 were begun by Hirn (1855) completed by Rubner ( x ) and Chau- 

 veau (1899), and confirmed by Atwater's experiments. The work 

 of Atwater's school has been considerable ; its general results 

 being contained in Bulletins, Nos. 136 (1903) ; 175 (1907), and 

 208 (1909). 



The experimental method adopted by Atwater may briefly be 

 described as follows ( 2 ) : 



The subject is placed in a caloiimetric chamber of about 

 5 metres cube, this although a somewhat limited space causes no 

 inconvenience for a single visit. ( 3 ) The walls of the chamber are 

 covered with a system of small tubes in which water at a known 

 temperature of entry can be circulated. The water tube system 

 absorbs the heat radiated from the body of the subject. The air 

 in the chamber is renewed by a centrifugal fan. and arrangements 

 are made so that periodical samples of the air can be taken both 

 at its inlet and its outlet. The heat evolved can be accurately 

 evaluated by measuring the increase of temperature in the water, 

 which can be read to an accuracy of one-hundredth of a degree. 



Analysis of the gases and the volume of the circulating air 

 gives the weight of oxygen consumed and of carbonic acid gas 

 exhaled. The proportion of water vapour in the air before and 



(*) Rubner (Zeitsch. f. Biol., vol. xxx., 1894). 



( a ) Details of the apparatus are given in the 792 octavo pages of the above- 

 mentioned Bulletins. A clear and methodical summary has been given 

 by Jules Lefeure in his remarkable Trait ^de Bio6nerg6tique (p. 165, sqq], a 

 work already quoted. 



(*) A slight reservation must be made on this point, when the subject 

 is doing any considerable work (see Bulletin, No. 136, pp. 81 and 109). 



