62 PHYSIOLOGICAL CHEMISTRY. 



oxygen being present in smaller quantity ; and secondly, by their large 

 proportion of carbon, which constitutes on the average a little over 75 

 per cent, of their weight. This fact is probably connected with their 

 inflammability, the oils being oxidized at a temperature of 300 C., and 

 burning with a bright flame. The smooth consistency of oleaginous 

 matters is also one of their distinguishing features, and enables them 

 to be employed as lubricating substances, to diminish the friction be- 

 tween opposite surfaces. In the pure condition they are destitute of 

 taste and odor. They are all liquid at moderately high temperatures, 

 and solidify by crystallization when cooled down to a certain point, 

 which is different for each variety. The fatty substances which at or- 

 dinary temperatures have a thick, solid, or semi-solid consistency, are 

 more especially designated as " fats ;" those which are more liquid are 

 spoken of as "oils." They have no rotatory action on polarized light. 

 They are insoluble in water, and do not mix with it except by mechan- 

 ical agitation ; after which the two fluids separate from each other ac- 

 cording to their specific gravity, the water remaining below and the oil 

 rising to the surface in a distinct layer. Fats and oils are slightly 

 soluble in alcohol, and freely soluble in ether, which is used to extract 

 them from admixture with other organic substances. 



Fatty matters are found in varying quantity in different vegetable 

 tissues, the most abundant deposit occurring in nuts, fruits, and seeds, 

 particularly those of the sweet and bitter almond, the chocolate tree, 

 hemp, flax, Bicinus communis, and Croton tiglium, in which last it is 

 in the proportion of 60 per cent. The seeds of plants generally are 

 designated as "starchy " or "oleaginous," according to the preponder- 

 ance of one or the other of these substances in their tissue. In the 

 animal body, fat is most abundant in the adipose tissue and in the mar- 

 row of the long bones, where it amounts to from 80 to 96 per cent. 

 In the human subject, under normal conditions, the entire quantity of fatty 

 matters has been estimated at from 2.5 to 5 per cent, of the bodily weight.* 



The following list gives the proportion of fat in various alimentary 

 substances, according to the tables of Payen : 



QUANTITY OF FAT IN 100 PAETS IN 



Wheat . . . 2.10 Beef's flesh (average) 5.19 



Indian corn . . 8.80 Calf 'sliver . . 5.58 



Potatoes . . . 0.11 Mackerel . . . 6.76 



Beans. . . . 2.50 Salmon . . . 4.85 



Peas .... 2.10 Oysters . . . 1.51 



Sweet almonds . . 24.28 Cow's milk . . 3.70 



Chocolate nut . . 49.00 Fowl's egg . . 7.00 



Beside entering as an ingredient into the above articles, fat is often 

 taken with the food in a pure, or nearly pure, form, as butter, olive oil, 

 or adipose tissue. 



Origin of Fatty Substances. The first production of these organic 



*Gorup-Besanez: Physiologischen Chemie. Braunschweig, 1878, p. 169. 



