CHEMICAL COMPOSITION OF THE BODY. 



97 



margarin is a mixture df tripalmitin and tristearin. A separation of these 

 proximate principles within the cells may occasionally be observed at low 

 temperatures; the more solid fats, tripalmitin and tristearin, appearing as 

 a minute stella of crystalline form, surrounded by the still fluid triolein. 

 The mean percentage composition of human fat is C 76.62, H 11.94, O 11.44. 

 expressed by the empirical formula C C ,H 99 O,.. Exposed to the action of 

 superheated steam, they break up into the fatty acids and glycerin. All 

 the animal fats are soluble in hot alcohol, in ether, fluid oils, benzole, car- 

 bon disulphide, and in chloroform. They are distinguished from one 

 another by the temperature at which they respectively solidify, and by the 

 salts that they form with the alkalies. 



The following table shows about the proportion in which they are found 

 in some of the fluids and tissues of the body : 



Sweat, . . . . 

 Vitreous humor, 

 Saliva, . . . 

 Lymph, 

 Synovia, . 

 Liq. Amnii, . . 

 Chyle, . . . . 

 Mucus, 



Percentage 

 of fat, 



0.001 



0.002 



002 



0.05 



0.06 



0.06 



0.2 



0.3 



Milk, 



Cortex of Brain, . 

 Brain (whole), . 

 Hen's Egg, . . . 

 Medulla of Brain, 

 Nerves, . . . 

 Spinal Cord, . . 

 Adipose Tissue, . 



Percentage 

 of fat. 



. . 4.3 

 5.5 



8.0 

 11.6 



20. 



22.1 



23.6 



82.7 



f ' TT 1 



CHOLESTERIN, ^ 43 >O-fH 2 (or biliary fat), 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, the ob- 

 tuse angle being 100 30', the acute 79 30' : it is quite insoluble in water, 

 but is soluble in ether, and also in boiling alcohol, from which, however, the 

 greater part separates on cooling. It does not melt until heated to 298, 

 and it solidifies again and becomes perfectly crystalline at 275. It is not 

 decomposed by concentrated alkalies even when the mixture is submitted to 

 prolonged heat. It is found in plants, 1 and is constantly present in the 

 blood, in the proportion of about two parts in ten thousand ; its quantity 

 seems to be augmented in old age. It is found also in the lymph, in most 

 glands, and is stated to be a constituent of the nervous tissue, being proba- 

 bly a product of the disintegration of the nerve-substance. It is frequently 

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

 considerable quantity in dropsical fluids, and particularly in the contents of 

 cysts. It is occasionally seen in disorganized eyes, floating in detached scales 

 in the fluid vitreous, and is sometimes deposited in the solid form in de- 

 generated structures, tubercular concretions, etc. Strong arguments have 

 been adduced by Dr. Austin Flint 2 for regarding it as an excrementitious 

 principle discharged by the liver, and hardly second in importance to urea. 

 He has found it always more abundant in the blood returning from the 

 brain than elsewhere ; also that its quantity is exceedingly small in the 

 venous blood of the paralyzed side in hemiplegia ; and that in cases of seri- 

 ous structural disease of the liver, accompanied by symptoms pointing to 

 blood-poisoning, cholesteriu accumulates in the blood, constituting a condi- 

 tion which he has called Cholesterremia. 



STERCORIN. This term has been applied by Dr. Austin Flint to a pecu- 

 liar substance, crystallizing in needles, which may be extracted from normal 

 fteces by the successive action of ether, alcohol, and a hot solution of caustic 

 potash, by which all the saponifiable fats are removed. On largely diluting 



1 Beneke, Annalen, Band cxxii, p. 249, and cxxvii, p. 105. 



2 Physiolog-y of Man, vol. ii, p. 402. 



