74 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



to possess, of promoting the nutrient processes in individuals laboring under 

 tuberculous cachexia, can scarcely be attributed to anything else than to its 

 furnishing an abundant supply of fatty matters in a form that renders them 

 peculiarly easy of assimilation. Taking all these facts into account, we seem 

 justified in accepting the conclusion, that in the metamorphosis of the albumi- 

 nous constituents of the food into the organized tissues, of which they are the 

 I roper pabulum, fat takes an essential part; and thus it comes to have a much 

 igher place in the economy of the living system than has usually been assigned 

 to it. 1 



43. Of the non-saponifiable fats, or "lipoids," there are two which appear to 

 be normal constituents of the blood; though it is doubtful whether they are 

 ever employed in the formation of tissue, and whether they are not rather to 

 be looked on as excrementitious products, resulting from the disintegration of the 

 living structure. Cholesterin (or biliary fat), the most important of these, is 

 a hard spermaceti-like substance, which separates from its solutions in nacreous 

 scales that are found under the microscope to have the form of rhombic tablets ; 

 it is quite insoluble in water, but is soluble in ether, and also in boiling alcohol, 

 from which, however, the greater part separates in cooling; it. is also slightly 

 soluble in soap-water, and more freely in the fatty oils and in taurocholic acid. 

 It does not melt until heated to 298, and it solidifies again and becomes per- 

 fectly crystalline at 275. It is not decomposed by concentrated alkalies, even 

 when the mixture is submitted to prolonged heat. Its composition is represented 

 by the formula 37C, 32H, 0; but its combining equivalent is as yet uncertain. 

 Cholesterin is constantly present in the blood, to the amount of from .025 to .2 

 parts in 1000 (that is, from ^th to jth of one-thousandth part of the whole 

 mass) ; and its quantity seems to be augmented in old age, and in many acute 

 diseases, as also in icterus. It is also stated to be a constituent of the nervous 

 tissue, having been extracted from the brain by Couerbe and, other experiment- 

 ers; but it may be doubted whether it is not rather a product of the disintegra- 

 tion of nerve-substance, which is destined to be taken back into the blood for 

 elimination by the excretory apparatus, like the kreatine which may be extracted 

 from the juice of flesh ( 60), or the urea which is obtainable from the vitreous 

 humor of the eye ( 53), both being undoubtedly excrementitious matters. 

 For Cholesterin is a characteristic component of the biliary excretion, and is 

 closely related to its peculiar acids; 2 so that it can scarcely be looked upon in 

 any other light than as an excrementitious product, the highest function of 

 which is to assist in the support of the calorifying process. It is frequently 

 separated from the blood as a morbid product; thus it is often present in con- 

 siderable quantity in dropsical fluids, and particularly in the contents of cysts; 

 and may be deposited in the solid form in degenerated structures, tubercular 

 concretions, &c. Of the other non-saponifiable fat, termed Serolin, much less 

 is known. It is obtained from the serum of blood, after the removal of the 

 other fats; and seems to differ from cholesterin chiefly in having a lower nielt- 



1 It was first discovered by Ascherson, that when an oil-globule is surrounded by an 

 albuminous solution, it becomes invested by a pellicle of coagulated albumen ; and he went 

 so far as to present this as the type of cell-formation in the living body. In this, however, 

 he was undoubtedly in error; for the passive coagulated albuminous pellicle thus formed 

 has nothing in common with the activity of a true cell ; and it may be generated, more- 

 over (as shown by Mulder), around other substances, gum arabic, for instance. In con- 

 nection with this subject, the Memoir by Prof. Bennett on "the Structural Relation of 

 Oil and Albumen in the Animal Economy," in the "Edinb. Monthly Journ. of Med. Sci." 

 vol. viii. p. 566, and his work on Cod-liver Oil, may be advantageously referred to. 



2 By the action of oxidizing agents upon Cholesterin, a peculiar acid, cholesteric acid, 

 is obtained; and the same acid (as shown by Schlieper) may be obtained in the same way 

 from the resinous acids of the bile, and from no other organic substance whatever. (See 

 Liebig's "Familiar Letters," p. 440, note.) 



