138 LIFE AND DEATH. 



is a real food, biothermogenic for certain vegetable 

 organisms. But urea is also a food for micrococcus 

 urecs. It does not follow that it is a food for mann- 

 mals. We have not reached the solution yet — adJiuc 

 sub judice. 



Conclusion : The Energetic Character oj Food. — To 

 sum up we have confined ourselves, in what has been 

 said, to the consideration of a single character of 

 food, and really the most essential, its energetic 

 character. Food must furnish energy to the organism, 

 and for that purpose it is decomposed and broken up 

 within it, and issues from it simplified. It is thus, 

 for instance, that the fats, which from the chemical 

 point of view are complicated molecular edifices, 

 escape in the form of carbonic acid and water. And 

 so it is with carbo-hydrates, starchy and sugary 

 substances. This is because these compounds 

 descend to a lower degree of complexity during their 

 passage through the organism, and by this drop, as it 

 were, they get rid of the chemical energy which they 

 contained in the potential state. Thermo-chemistry 

 enables us to deduce from the comparison of the 

 initial and final states the value of the energy 

 absorbed by the living being. This energetic, dynamo- 

 genie or thermogenic value, thus gives a measure of 

 the alimentary capacity of the substance. A gramme 

 of fat, for instance, gives to the organism a quantity 

 of energy equivalent to 9.4 Calories ; the thermo- 

 genic value of the albumenoids is 4.8 Calories. 

 The thermogenic or thermal value of carbohydrates 

 is less than 4.7 calories. This being so, we under- 

 stand why the animal is nourished by foods which 

 are products very high in the scale of chemical 

 complexity. 



