PREFACE. XV 



How clear are now to us the relations of the 

 different articles of food to the objects which they 

 serve in the body, since organic chemistry has 

 applied to the investigation her quantitative method 

 of research ! 



When a lean goose, weighing 4 Ibs., gains, in 

 thirty-six days, during which it has been fed with 

 241bs. of maize, 51bs. in weight, and yields S^lbs. of 

 pure fat, this fat cannot have been contained in the 

 food, ready formed, because maize does not contain 

 the thousandth part of its weight of fat, or of any 

 substance resembling fat. And when a certain 

 number of bees, the weight of which is exactly 

 known, being fed with pure honey, devoid of wax, 

 yield one part of wax for every twenty parts of 

 honey consumed, without any change being percep- 

 tible in their health or in their weight, it is impossi- 

 ble any longer to entertain doubt as to the forma- 

 tion of fat from sugar in the animal body. 



We must adopt the method which has thus led to 

 the discovery of the origin of fat, in the investiga- 

 tion of the origin and alteration of the secretions, as 

 well as in the study of all the other phenomena of 

 the animal body. From the moment that we begin 

 to look earnestly and conscientiously for the true 

 answers to our questions, that we take the trou- 

 ble, by means of weight and measure, to fix our 



