CONDITIONS ESSENTIAL TO NUTRITION. 41 



large quantity of hydrogen and oxygen in the 

 same proportion^ as in water. It also contains 

 in solution, lactate of soda, phosphate of lime, and 

 common salt ; and a peculiar aromatic product 

 exists in the butter, called butyric acid. The 

 knowledge of the composition of milk is a key to 

 the conditions necessary for the purposes of nutri- 

 tion of all animals. 



All substances which are adequate to the nourish- 

 ment of animals, contain those materials united, 

 though not always in the same form ; nor can 

 any one be wanting, for a certain space of time, 

 without a marked effect on the health being pro- 

 duced. The employment of a substance as food, 

 presupposes a knowledge of its capacity of assimi- 

 lation, and of the conditions under which this takes 

 place. 



A carnivorous animal dies in the vacuum of an 

 air-pump, even though supplied with a supera- 

 bundance of food ; it dies in the air, if the demands 

 of its stomach are not satisfied ; and it dies in pure 

 oxygen gas, however lavishly nourishment be given 

 to it. Is it hence to be concluded, that neither 

 flesh, nor air, nor oxygen, is fitted to support life ? 

 Certainly not. 



From the pedestal of the Trajan column at 

 Rome, we might chisel out each single piece of 

 stone, if, upon the extraction of the second, we re- 

 placed the first. But could we conclude from this, 

 that the column was suspended in the air, and not 



