THE REPRODUCTIVE GLANDS. 445 



digestion, and hence probably consist of albumins. As a whole 

 the spermatozoa are exceedingly resistant to ordinary solvents. They 

 are soluble in boiling solutions of the caustic alkalies, while in 

 concentrated sulphuric acid, nitric acid, acetic acid, and boiling 

 solutions of sodium carbonate they dissolve only in part. They 

 are likewise resistant to putrefactive changes, and can be obtained 

 from dried semen, with the preservation of their natural form, 

 by placing the material in a 1 per cent, solution of sodium chloride. 



The Ovaries. Thus far a study of the chemical composition 

 of the ovaries has not revealed any special points of interest. 

 In addition to collagen and mucins, which enter into the con- 

 struction of the supporting tissue of the organs, nucleins and true 

 albumins have also been found, and are probably derived from the 

 contained ova and other cellular elements. 



The most important constituents of the cortex of the gland, viz., 

 the Graafian follicles, which enclose the specific product of the func- 

 tional activity of the ovaries, viz., the ova, have for obvious reasons 

 not been open to a detailed investigation. The contained fluid 

 is apparently serous in character. After the discharge of the 

 ova the remaining follicles are first filled with blood from the torn 

 vessels of the vesicle, and are subsequently transformed into the 

 so-called corpora lutea. The yellow color of these is owing to lipo- 

 chromes, or luteins, of which an amorphous and a crystalline form 

 may be isolated (see also page 462). 



The Ovum. Of the chemical composition of the ova of the 

 human being and mammals in general, nothing definite is known, 

 as it is impossible to collect them for purposes of analysis. The 

 eggs of fishes, amphibia, reptiles, and especially of birds, on the 

 other hand, can readily be obtained and have been studied in greater 

 detail. In the following pages we shall confine our attention to 

 the composition of birds' eggs, which is best understood. The egg 

 proper is here surrounded by the so-called white of egg, which in 

 turn is enclosed in a double membrane, and is covered by the shell. 

 These additional structures, however, are not formed in the ovary, 

 but are produced during the passage of the egg through the oviduct 

 from material, which is here secreted by the lining cells. 



The Shell. The shell consists essentially of an organic matrix of 

 the character of keratin, which is largely impregnated with lime 

 salts. Of these, calcium carbonate is the most abundant, and con- 

 stitutes about 90 per cent, of the weight of the entire shell. In 

 addition, we find a small amount of magnesium carbonate, as also 

 phosphates of both elements. Water is present to the extent of 

 only about 1 per cent. The pigments met with in birds' eggs 

 are closely related to the biliary pigments, and, like these, are 

 derived from the common pigment of blood. The oorhodein, which 

 presents a reddish or brownish-red color, is supposedly identical 

 with hsematoporphyrin ; while the blue or green pigment, which is 



