62 PHYSIOLOGICAL CHEMISTRY. 



characteristic appearance. The function of lecithin in the 

 body is not understood, but from the fact o>f its wide distri- 

 bution and its occurrence in milk it is reasonable to assume 

 that it performs some important part. 



The Waxes. These bodies bear some resemblance to the 

 fats and will be briefly mentioned here. They consist largely 

 of esters of the higher monohydric alcohols of the saturated 

 series, and in most cases are complex mixtures of which the 

 composition is not exactly known. Spermaceti seems to con- 

 sist largely of cetyl palmitate, C 10 H 33 OC 16 H 31 O. Beeswax 

 contains some free acid, cerotic acid, in addition to the esters. 

 The most important constituent is apparently myricin or 

 myricyl palmitate, C 30 H 61 OC 16 H 31 O. The waxes are not 

 easily saponified and as a rule clear soap solutions are not 

 obtained. 



Cholesterol. This substance is an alcohol, but in appear- 

 ance it resembles some of the solid fats and is associated with 

 them in several natural products. Hence it is in place to 

 describe it here. The formula C 27 H 45 OH probably repre- 

 sents the composition of the body which is found in the brain, 

 yolk of egg, the liver, blood and other tissues and is especially 

 abundant in the fat of wool. It constitutes also the main 

 substance in certain gall-stones from which it may be sepa- 

 rated in nearly pure condition. In wool fat it exists partly in 

 the free state and partly in combination with fatty acids in 

 the form of esters. 



It is readily soluble in hot alcohol, ether, benzene and chloro- 

 form, but not in water or alkali solutions. It is therefore left 

 as an insoluble residue in the saponification of fatty mixtures 

 containing it. Under the microscope pure cholesterol appears 

 as a mass of white plates with sharp angles. The cholesterol 

 esters combine with water to form stable emulsions, and it is 

 probably on account of the presence of these esters that the 

 substance known as lanolin is practically valuable. This lano- 

 lin is made from purified wool fat and is largely used in the 

 preparation of salves and ointments. 



