ALIMENTARY ENERGETICS. 131 



identical with its theoretical thermogenic value. In 

 this case it might be determined experimentally by 

 direct calorimetry, measuring the heat produced by 

 the animal supposed absolutely unchanged and iden- 

 tical before and after the consumption of the food. 



3. DIFFERENT TYPES OF FOODS. THE REGULAR, 

 BlOTHERMOGENIC TYPE AND THE IRREGULAR, 

 THERMOGENIC TYPE. 



Food is a source of thermal energy for the organ- 

 ism because it is decomposed within it, and undergoes 

 within it a chemical degradation. Physiological 

 chemistry tells us that whatever be the manner in 

 which it is broken up, it always results in the same 

 body and always sets free the same quantity of heat. 

 But if the point of departure and the point of arrival 

 are the same, it is possible that the path pursued is 

 not constantly identical. For example, one gramme 

 of fat will always give the same quantity of heat, 

 94 Calories, and will always come to its final state 

 of carbonic acid and water ; but from the fat to 

 the mixture of carbonic acid gas and water there 

 are many different intermediaries. In a word we 

 get the conception of varied cycles of alimentary 

 evolutions. 



From the point of view of the heat produced it has 

 just been said that these cycles are equivalent But 

 are they equivalent from the vital point of view? 

 This is an essential question. 



Let us imagine the most ordinary alternative. 

 Food passes from the natural to the final state after 

 being incorporated with the elements of the tissues, 



