78 THE FATS. 



the yolk of eggs it occurs in combination with vitellin, but is here 

 apparently not closely bound. A certain similarity thus exists 

 between the lecithins and the nucleins ; both contain phosphorus 

 in their molecules, and both combine with albumins to form more 

 complex substances. The lecithins occur widely distributed in both 

 the animal and vegetable world. According to Hoppe-Seyler, they 

 are found in all cells and bodily fluids. They are abundant in 

 nerve-tissue and also in the eggs and semen of most animals. Of 

 special interest is the fact that the activation of certain haemolytic 

 substances (tetanus toxin, solanin, saponin, cobra poison) is eifected 

 by means of lecithin, and that the hsemolytic complement in normal 

 blood-serum is probably of this nature (Kyes). 



W. Koch has recently pointed out the probable import in the 

 life of the cell of the lecithins, for which he proposes the collective 

 term lecithanes, and summarizes his conclusions as follows : 1. In 

 association with albumins, in colloid solutions they furnish the basis 

 for the establishment of the necessary viscosity, by the ease with 

 which they (the lecithanes) are influenced by ions (Na, Ca). 2. They 

 are concerned in the metabolism of the cell, and in consequence of 

 the presence of the unsaturated fatty acids they take part in the 

 oxygen metabolism and by means of their methyl groups united 

 to nitrogen in still other and unknown reactions. (Their isolation 

 and special tests will be considered in a subsequent chapter.) 



THE CHOLESTERINS. 



The cholesterins are monatomic alcohols of the formula C^H^.- 

 OH -f H 2 O. They are found in all animal cells, in the blood, 

 lymph, etc., and are especially abundant in nerve-tissue and in the 

 bile. In the gall-bladder they are frequently found in the form of 

 gall-stones, and not uncommonly constitute the greater portion of 

 their solids. Different varieties exist, such as the common choles- 

 terin of the concretions just mentioned, the isocholesterin of wool- 

 fat (lanolin), and the phytosterins, paracholesterins, and kaulosterins 

 of plants. While the structural composition of cholesterin has not 

 been definitely ascertained, there is evidence to show that it may be 

 a terpene. It is probably not formed as such in the animal body, 

 but results in some manner from the vegetable forms. Like the 

 fats, the cholesterins are insoluble in water, but soluble in ether, 

 alcohol, and chloroform, from which solutions they may be obtained 

 either in the form of very characteristic platelets or as needle-like 

 crystals. In solutions of the alkalies, in the absence of alcohol, 

 they are entirely insoluble, even on boiling, in which respect they 

 differ from the fats. Like glycerin, cholesterin combines with fatty 

 acids to form compound ethers, and in this form it is frequently 

 found in nature. In wool-fat, for example, it is thus present in large 

 amounts, and from it such ethers can be readily obtained. In pure 

 form they constitute the lanolin of the shops. These ethers show a 



