536 THE THEORY OF ENERGY AND THE LIVING WORLD. 



the potential energy which the plant has formed. Chemistry enables 

 us to compute the quantity of energy which an aliment thus disengages. 

 It applies Berthelot's principle of the initial and final state; and by 

 utilizing the numerical tables established by this eminent chemist with 

 such admirable patience, we obtain in calories the quantity of energy 

 which the aliment furnishes to the organism. Thus we know its dyna- 

 mogenic or thermal power. 



This energy, whose exact amount is now known for each category of 

 aliments, is made use of in accordance with the third principle. It is to 

 be transformed following two possible types. Jn the normal type it is 

 transformed first into vital energy (the physiological work of Chauveau) 

 and subsequently either into mechanical work (the movement of the 

 muscles) or into thermal energy (heat which is dissipated externally). 

 In this normal case the aliment has wholly accomplished its office, since 

 it has served to sustain the vital functions. It has been dynamogenic, 

 or bio-thermogenic. 



On the other hand, we have the possibility of the abnormal or aber- 

 rant type. It may happen that, in virtue of its chemical nature, and 

 for reasons just beginning to be understood, the aliment in its decom- 

 position liberates energy which the organism is unable to make use of, 

 and which in consequence is not transformed into vital energy or any 

 kind of physiological activity, but passes directly into the thermal 

 state. A category of such aliments might be mentioned, or rather a 

 list of substances of this nature, for they scarcely merit the name ali- 

 ment. Alcohol and the acids which exist in fruits, such as malic, and 

 citric acids fall in this type. They may be called pure thermogens. 

 Some physiologists — and their error has its origin in the common habit 

 of prejudgment — still imagine that alcohol is a generator of force, dan- 

 gerous, to be sure, on account of its abuse, but still a source of energy 

 as much as sugar or fat, and thus capable of furnishing part of the 

 energy necessary to the execution of difficult tasks. This is errone- 

 ous. To be sure, alcohol decomposes or is consumed in the organism, 

 and produces heat, but that only serves to be uselessly dissipated. The 

 heat produced within the body is no more efficacious than that which 

 comes from the heat of the climate or of our fires. The pure ther- 

 mogens are then exclusively employed in producing internal heating. 

 Aliments such as we have discussed under the name of bio-thermogens 

 are equally as much as these a source of internal heating, but also par- 

 ticipate in the vital functions. 



In saying that the cycle of energy which runs its course in the ani- 

 mal organism takes its departure in the chemical disintegration of the 

 aliment, physiologists employ a formula too general and not sufficiently 

 approximate to the truth. Hence there have arisen confusion, misun- 

 derstandings, and controversies, which revive continually and give to 

 this branch of physiology an appearance of being in an unsettled and 

 disordered condition, which ought not to exist. It is not the vital 

 activity in its generality which should be considered when one wishes 



