170 OILS AND FATTY MATTER. 



pies, each of which is convertible, by a caustic alkali, into a fatty acid, 

 saccharine matter, called glycerine, and water ; they have, therefore, 

 been called kydrated salts of glycerine. Some of the acids are termed 

 fixed acids, and others are odorous, volatile, and acrid. Many of the 

 oily seeds and nuts are very indigestible, and being non-nitrogenized 

 foods, they are thought to be incapable of transformation into food ; 

 but are employed in the process of respiration. 



Liebig maintains that fat may be formed in the body by sugar and 

 starch. It is quite certain that animals derive fat chiefly from vegetables, 

 both by the process of assimilation and from the original oil many are 

 known to contain. The chyle at all times, whether feeding on vege- 

 table or animal food, contains floating globules of oil ; and the adi- 

 pose, as well as the nervous tissues, obtain their fatty parts from the 

 blood. The relative amount of oily matters in the system constitute 

 marked differences in the appearance, the leanness and obesity of in- 

 dividuals. Gall-stones have been attributed to the imperfect assimila- 

 tion of oily substances. But, notwithstanding the use of oily substan- 

 ces have been much condemned, they are important elements of food, 

 and they are found, in many cases, highly useful, even to diabetic pa- 

 tients. They afford, when they agree with the stomach, a sensation 

 of satisfaction and support not experienced from other food. Butter 

 is more especially an agreeable form of oleaginous food. This is ex- 

 tensively produced in the U. S. 600,000 pounds are annually ex- 

 ported to the W. Indies. For this purpose it is clarified before it is 

 salted, by placing it in a vessel surrounded by water within another 

 vessel, and slowly heating it until melted. After standing for parts 

 to settle, it is turned off, cooled and salted. Butter may be preserved 

 by covering it, when packed, with brine, in which has been dissolved 

 a small portion of saltpetre. Oil is .digested with difficulty in most 

 cases ; and although," says Dr. Pereira, it has been said by some 

 writers, that, taken as a condiment with salads, it promotes their di- 

 gestion, yet I do not coincide with them." Bone oil, it is said, when 

 taken with salads, is less likely to disturb the stomach than the same 

 or other oily or fatty substances when cooked. Olive or sweet oil will 

 be noticed in the next volume, under the head of that fruit, with the 

 other vegetable oils. 



The volatile oils, which belong exclusively to the vegetable kingdom, 

 are a constituent, as we have seen, of many plants served at table in a 

 raw state, and of the labiate plants generally, as with the seasoning 

 herbs, such as mint, savory, thyme, majoram, &c, This oil is con- 

 tained in small cells within the leaves. The aromatic seeds and leaves 

 of many of the umbelliferous plants, such as anise, carroway, fennel, 

 &c. are also seen to contain this oil ; and it is to it that they, with 

 the preceding, owe their flavor. This oil, in the latter plants, is con- 

 tained in tubular vessels called vitta, within the pericarp of the fruit. 



