THE REPRODUCTIVE GLANDS. 453 



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 fats. In birds' eggs 

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

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

 vitellorubin, 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. 



ISOLATION. To isolate the lecithins, the method of Ziilzer may 

 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 off, 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 

 on the filter is dissolved in as little ether as possible, and precipi- 

 tated with acetone. The precipitate is collected on a filter and 

 washed with acetone until the wash-acetone dissolves no more 

 cholesterin. The residue is again dissolved in a small amount of 

 ether or benzol. To this solution an excess of absolute alcohol is 

 added, when on standing a white amorphous substance separates 

 out, which can be obtained in crystalline form by solution in hot 

 alcohol and cooling ; this apparently consists of tripalmitin. After 

 filtration the pure lecithin can then be obtained from the ether- 

 alcoholic solution by precipitating with acetone, as before, or by dis- 

 tilling off the alcohol and ether. The resulting material is dried in 

 the vacuum. Its phosphorus varies between 3.7 and 4.1 per cent, 

 in amount. 



Incubation. Of the chemical changes which take place during 

 the process of fertilization, and in which the nucleus of the ovum is 

 primarily concerned, we know nothing. But there can be no doubt 

 that, in fishes at least, the protamin radicle of the nucleins of the 

 spermatozoa plays an important part. As a result, the reproductive 

 function of the ovum, which previously has remained dormant, 

 now manifests itself in the mysterious morphological changes which 

 the cell undergoes, and which end in the production of an organism 

 that is morphologically and chemically like its parents. 



In mammals the food-stuffs which are required by the devel- 

 oping organism are constantly supplied through the blood of the 

 mother-animal, but in the lower forms of life they are furnished 



