FATS AND OILS. 



183 



with water, giving it a consistence called mucilaginous. They have the same composition 

 as starch. 



Experiments have shown that gum passes through the alimentary canal unchanged 

 and has no nutritive power. 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 exudation is impure and contains many other substances. Gum 

 is mentioned in this connection from the fact that it is frequently 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 the animal and the vegetable 

 kingdom, constitute an important division of the articles of food. As a proximate prin- 

 ciple, fat is found in all parts of the body, with the exception of the bones, teeth, and 

 fibrous tissues. It necessarily constitutes an important part of all animal food and is 

 taken in the form of adipose tissue, infiltrated in the various tissues in the form of globules 

 and granules of oil, and in suspension in the caseine and water in milk. Animal fat is a 

 mixture of oleine, margarine, and stearine, in varied proportions, and possesses a con- 

 sistence which depends upon the relative quantities of these principles. More or less fat 

 always enters into the composition of food, but, as a rule, it is more abundantly taken in 

 cold than in warm climates. The ordinary diet of the Greenlander contains what would 

 be considered in temperate climates as an enormous quantity of fat and oil, frequently in 

 a disgusting form, and often taken unmixed with other articles. 



The different varieties of animal fats do not demand special consideration as articles 

 of diet. Butter, an important article of food, is somewhat different from the fat extracted 

 from adipose tissue, but most varieties of fat lose their individual peculiarities in the pro- 

 cess of digestion and are apparently identical when they find their way into the lacteal 

 vessels. 



FIG. 45._ Crystals of margarine and mar- 

 garic acid. (Funke.) a, a, a, margarine ; 

 &, margaric acid. 



FIG. 46. Crystals of stearine and stearic 

 acid. (Funke.) a, a, a, stearine; &, 

 stearic acid. 



In the vegetable kingdom, fat is particularly abundant in seeds and grains, but it 

 exists in quantity in some fruits, as the olive. Here it is generally called oil. Its pro- 

 portion in linseed is 20 per cent. ; in rape-seed, 35 to 40 per cent. ; in hemp-seed, 25 per 

 cent. ; and in poppy-seed, 47 to 50 per cent. It exists in considerable proportion in nuts 

 and in certain quantity in the cereals, particularly Indian corn. Its proportion in the 

 different varieties of wheat is from 1'87 to 2'61 per cent. ; in rye, 2'25 per cent. ; in 

 barley, 2'76 per cent. ; in oats, 5'5 per cent. ; in Indian corn, 8-8 per cent. ; and in rice, 

 0'8 per cent. The above is the proportion in the grains after desiccation. 



Fat, both animal and vegetable, may be either liquid or solid. It has a peculiar oily 



