FATS. 69 



with certain nitrogenous organic matters of an albuminous nature. 

 White of egg, or the serum of blood, exerts this effect in an energetic 

 manner, and the fatty substances of milk are held in suspension by its 

 liquid albuminous ingredients. 



Another characteristic of the true fatty substances is their property 

 of saponification, that is, of forming soaps when subjected to certain 

 chemical influences. If either of the natural fats be boiled for a con- 

 siderable time in the watery solution of a free alkali, it is decomposed, 

 with the production of two new bodiesfirst, glycerine (C 3 H 8 3 ), a neu- 

 tral fluid substance which is soluble in water; and secondly, a fatty 

 acid which combines with the alkali and forms a soap. An analogous 

 change is thought to take place with a portion of the fatty matters in 

 the animal fluids. 



The fats are derived from both the animal and the vegetable world. 

 They are present in many of the solids and fluids of the living body, 

 and are found also in many varieties of vegetable food. The following 

 list gives the proportion of fat in various alimentary substances, accord- 

 ing to the tables of Payen : 



QUANTITY OF FAT IN 100 PARTS IN 



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



Indian corn . . . 8.80 Calf's liver . . . 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 the various kinds of adipose tissue. 



Fat is produced in the vegetable tissues, perhaps to some extent 

 directly from carbonic acid and water, but certainly in considerable 

 quantity by transformation of the starch originally formed. 1 It is from 

 this source that the fat so abundantly stored up in oily seeds and fruits 

 is mainly derived; and in this situation it is retained until required for 

 the purposes of germination and growth. It is accumulated in some 

 seeds and fruits in remarkable quantity, particularly in those of the 

 sweet and bitter almond, the chocolate tree, hemp, flax, ricinus com- 

 munis, and Croton tiglium, where it exists in the proportions of from 

 24 to 60 per cent. 



The three most important varieties of fat are those known as Stearins, 

 Palmitine, and Oleine. They resemble each other in their general 

 characters, and differ mainly in their degree of fluidity at correspond- 

 ing temperatures ; stearine solidifying the most readily of the three, 

 while oleine remains fluid at a lower temperature than either of the 

 others. 



1 Mayer, Agrikultur-Chemie, Band i. pp. 84, 85. 



