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fibrine, and caseine ; and these three principles have a strict 

 chemical identity with what are found in vegetable substances, 

 under the names respectively of vegetable albumen, gluten, 

 (when in a pure state), and vegetable caseine. These are 

 the principles which, though present in vegetable substances 

 in but small proportion, are yet the most abundant in those 

 which are best adapted as food for animals, and such as are 

 most nutritious ; for instance, in the grains of the various 

 cerealia, peas, beans, &c. ; and it is very interesting to 

 observe, (as affording an evident instance of special adapta- 

 tion,) that such substances likewise particularly abound in 

 those earthy salts which enter into the composition of the 

 bodies of animals, and form the chief part of the more solid 

 organs of support — the bones, and which are, therefore, 

 required to be present in their food. Other vegetable 

 aliments, which contain much less of these azotized prin- 

 ciples, (such as potatoes, turnips, carrots, clover, hay, &c.,) 

 are less nutritious, and a larger amount is required to afford 

 a satisfactory meal. Thus, a horse eats a much larger 

 quantity of hay to satisfy its appetite than it would of oats, 

 or other corn. But besides these azotized principles, animal 

 bodies possess some chemical compounds which contain no 

 nitrogen ; such are the animal fats and gelatine ; and by 

 far the greater part of all vegetable growths consist of 

 non-azotized principles ; such are starch, gum, sugar, and 

 vegetable fixed oils, which are much employed as aliment 

 for man and other animals, (though less nutritious than the 

 azotized principles previously mentioned,) and lignin, which 

 is commonly not regarded as an alimentary principle. 



With these facts before him, Liebig has been led to 

 consider the converting powers of the digestive organs of 

 herbivora, as being much more limited than has been sup- 

 posed to be the case by former physiologists ; and maintains 

 that in the food of herbivora, it is only that amount of the 

 azotized principles, identical with those in the tissues of 



