THE NORMAL QUANTITY OF FOOD. 409 



riments afford very slight indications of the quantities of food which 

 are necessary to maintain the animal in perfect health and in the 

 full use of its powers. When we deprive an animal of all food, all 

 its functions become impaired, both in their intensity and extent ; 

 and abnormal symptoms frequently occur, such as diarrhoea, stases 

 of blood in the different systems of capillaries, &c. ; if, therefore, 

 we wish to make the excretions of such animals a measure by 

 which to judge of the quantity of food indispensable to life, we must 

 remember that this measure would scarcely suffice to afford the 

 organism more than a scanty existence, for, as we have already 

 stated, the functions of the organs, the manifestations of force, and 

 the metamorphosis of matter connected with it, are totally different 

 in a state of repletion and in inanition. Such experiments are 

 nevertheless of high value to science. 



But how can the smallest quantity be discovered for an 

 amount of food which may give the organism the full use of its 

 faculties? If the absorption of nutrient matters in the intestine, 

 that is to say, the absorption of digested matters were limited to a 

 greater extent than it really is, if no more nutrient matters entered 

 the blood than were necessary for the reproduction of the tissues 

 and of the various functions, we might, perhaps, notwithstanding 

 some difficulties, calculate with tolerable exactness the amount of 

 food required for the organism, from a comparison of the excre- 

 tions and the food which had passed unchanged into the faeces. 

 Now we know, from our previous considerations, that the organism 

 is not able to convert an unlimited quantity of nutrient matter into 

 blood ; we always found that after partaking abundantly of any kind 

 of nutrient substance, some portion of it remained unchanged. The 

 exact determinations by weight, made by Boussingault in reference 

 to fat, those of Bidder and Schmidt in reference to the albu- 

 minates, and those of von Becker in reference to the carbo-hydrates, 

 prove that only definite quantities of these substances can be 

 resorbed by the intestine within a certain period of time. But 

 nature has also here given very wide limits to animal motions ; 

 thus, for instance, very many experiments show that the organism 

 is able to absorb through the intestinal capillaries and the lymph- 

 atics a much larger amount of nutrient matter or chyle, than it 

 requires for the restitution of the effete substances, or for the 

 accomplishment of different purposes of life. In overfeeding the 

 animal which is being experimented upon, a part of the food cer- 

 tainly passes unchanged into the excrements, but another portion 

 enters as superfluous nutrient matter into the blood, where it is 



