PREFACE. XXXI 



conditions most essential to the drawing of just 

 conclusions, could not be received as expres- 

 sions of the truth. 



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 41bs., gains, 

 in thirty-six days, during which it has been 

 fed with 241bs. of maize, 51bs. in weight, and 

 yields 3^ Ibs. of pure fat, this fat cannot have 

 been contained in the food, ready formed, be- 

 cause 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 

 perceptible in their health or in their weight, 

 it is impossible any longer to entertain a doubt 

 as to the formation 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 investigation of the origir* and alteration of 

 the secretions, as well as in the study of all 

 the other phenomena of the animal body. 



