NON-NITEOGENIZED AJLIMENTAJBY PRINCIPLES. 61 



cipitated in a gelatinous form from the juices of fruits by 

 alcohol. 



Mannite is a sweetish principle found in manna, mush- 

 rooms, celery, onions, and asparagus. Manna in tears is 

 composed of this principle in nearly a pure state. It is 

 perhaps more analogous to sugar .than to starch, but is not 

 capable of fermentation and has no influence on polarized 

 light. 



Gums and mucilages may enter to a certain extent into 

 the composition of food, but they can hardly be considered 

 as alimentary principles. Gums are found exuding from cer- 

 tain trees, first in a fluid state, but becoming hard on exposure 

 to the air. A viscid, stringy mucilage is found surrounding 

 many grains, such as the flax-seed, quince-seeds, and exists in 

 various kinds of roots 'and leaves. Both gums and mucilages 

 mix readily with water, giving it a consistence called muci- 

 laginous. They have the same composition as starch. 



Experiments have shown that gum passes through the 

 alimentary canal unchanged, and has no nutritive power. 1 

 It is said that gummy exudations from trees form an im- 

 portant part of the food of certain savage African tribes ; 

 but it must be remembered that in this condition the exuda- 

 tion is impure and contains many other substances. Gum 

 is mentioned in this connection from the fact that it is fre- 

 quently used in the treatment of disease, and is thought by 

 many to possess nutritive properties. 



Fats and Oils. Fatty or oily matters, derived from both 



Boussingault, out of fifty grammes of pure gum fed to a duck, extracted 

 forty-six from the faeces. (Memoires de Chimie Agricole et de Physiologic, Paris, 

 1854, p. 232.) Dr. Hammond ascertained by experiments on his own person 

 that gum is not only innutritions, but, when taken in quantity, is irritating and 

 injurious. He attempted to live for ten days on pure gum and water, but was 

 forced to discontinue his experiment at the end of the fourth day, from excessive 

 hunger, extreme debility, and fear of inducing serious disease. (Experimental Re- 

 searches relative to the Nutritive Value and Physiological Effects of Albumen, 

 Starch, and Gum, when singly and exclusively used as Food. Trans. American 

 Med. Assoc., 1857.) 



