THE REPRODUCTIVE GLANDS. 429 



Levene found C, 52.44 ; H, 7.45 ; N, 15.96 ; S, 0.92 ; P, 0.65 ; Fe 

 and O, 22.58 per cent. On treating with alkalies a substance is 

 obtained from this latter form, which is quite similar in compo- 

 sition to avivitellinic acid, as is seen from the figures: 0,32.56; 

 II, 0; X, 14.03; S, 0.146; P, 10.34 per cent. It is termed ick- 

 thulin'u: (tcid (see also page 428). 



ISOLATION. To isolate the ovivitellin from the yolk, it is well to 

 employ a large number of eggs. The yolks are thoroughly mixed 

 with an equal volume of a 10 per cent, solution of sodium chloride, 

 and are completely extracted with ether, by shaking, vi/., until no 

 more coloring-matter can be removed, and the sodium chloride 

 solution has become perfectly transparent. This is then diluted 

 with twenty times its volume of water, and the ovivitellin thus 

 precipitated. To purify the substance further, it is dissolved re- 

 peatedly in a 10 per cent, saline solution, and reprecipitated with 

 water. It is washed finally with alcohol and ether, and dried over 

 sulphuric acid. 



The Fats. The fat of the yolk consists almost entirely of olein, 

 pnlmitin, and stearin. As a whole, it contains a somewhat smaller 

 amount of carbon than ordinary fat, which may be due to the pres- 

 ence of mono- and diglycerides, or to the presence of a fatty acid 

 which contains less carbon than usual. On saponification Lieber- 

 mann obtained 40 per cent, of oleic acid, 38.04 per cent, of palmitic 

 acid, and 15.21 per cent, of stearic acid. 



The lipochromes or luteins of the yolk can be isolated as follows : 

 the fats of the yolk are saponified by boiling with an alcoholic 

 solution of sodium hydrate. The alcohol is then evaporated. The 

 remaining solution is treated with calcium chloride, which trans- 

 forms the soluble sodium salts into the corresponding insoluble cal- 

 cium salts. On cooling, the soaps are extracted with petroleum- 

 ether, which takes up the lipochromes. On evaporation they are 

 then obtained in pure form. The entire process of isolation must 

 be carried on in the absence of daylight, as otherwise the pigments 

 are decomposed after being separated from the flits. In birds' eggs 

 a yellow lipochrome, vitelloltftein, is notably found, but, in addi- 

 tion, traces of a red 'pigment of the same order, which is termed 

 ritrllorubin, may also be encountered. This latter cannot well be 

 obtained by extracting the soaps with petroleum-ether directly, but 

 it is necessary previously to decompose these with a mineral acid. 



Lecithins. The general properties of the lecithins have been con- 

 sidered in a previous chapter (page 65). 



ISOLATION. To isolate the lecithins, the method of Zul/cr mav 

 be conveniently employed. To this end, the yolks of a large num- 

 ber of eggs (fifty or more) are first extracted with ether by shaking, 

 until the ethereal solution takes up no more pigment. The ethereal 

 extracts are united, the ether is distilled oil', and the oil filtered off 

 at the temperature of the body. This is best accomplished in a 

 thermostat. The yellow, somewhat frothy material which remains 



