4L'i; THE GLANDULAR ORGANS. 



The substance cannot be precipitated with the common mineral 

 acids, acetic acid, and potassium ferrocyanide, nor by salting with 

 sodium chloride, magnesium sulphate, or sodium sulphate. Tan- 

 nic acid, phosphotungstic acid, ammoniacal subacetate of lead 

 solution, alcohol, and ammonium sulphate, when added to satura- 

 tion, cause the substance to separate out. It is soluble in water, 

 and is not coagulated by boiling. On evaporating its solutions to drv- 

 ness it is rendered insoluble in cold water, but dissolves on boiling. 



ISOLATION. To isolate the ovomucoid, the albumen is diluted 

 with water, as above, slightly acidified with acetic acid, and boiled. 

 The coagulable albumins are thus coagulated and filtered off. The 

 filtrate, which still gives the biuret reaction, owing to the presence 

 of the mucoid, is concentrated and precipitated with alcohol, or 

 saturated with ammonium sulphate. The mucoid is filtered off and 

 can then be purified by repeated solution in water and reprecipita- 

 tion with alcohol. 



The Yolk. The yolk of the egg represents the ovum proper. It 

 is surrounded by a delicate membrane the membrana pellucida 

 which supposedly consists of keratin or a closely related substance. 

 Owing to the extensive development of the protoplasmic portion of 

 the cell proper, the germinal vesicle is found at the extreme periph- 

 ery of the yolk, immediately beneath the limiting membrane. It 

 occupies the centre of the discus proligerus or cicatricula, which 

 rests upon a flask-like cavity with a long, narrow neck that extends 

 to the centre of the yolk, and is occupied by the so-called irhjfe yolk. 

 This surrounds the cicatricula and also forms a layer along the pe- 

 riphery of the yolk, immediately beneath the vitelline membrane. 

 It contains albumins, nuclei ns, lecithins, potassium salts, and possibly 

 also traces of glycogen, though this is doubtful. 



When broken, the yolk constitutes a creamy, viscid material, of 

 an orange-yellow color, which forms an emulsion with water, and is 

 coagulated by alcohol and on boiling. Its reaction is feebly alka- 

 line. On microscopical examination it is seen to consist of innumer- 

 able spherules, some of which are rich in fats and lipochromes, 

 while others, which are smaller, are colorless, transparent, semi- 

 crystalline structures of an albuminous character. In the eggs of 

 certain amphibia and fishes distinctly crystalline bodies are further 

 met with, which are spoken of as yolk platelets, and are analogous 

 to the aleuron granules of seeds. As has already been mentioned, 

 they probably consist of a compound of albumins with lecithins and 

 nucleins. The ichthidin, which is found in carp eggs, and which in 

 amorphous form is known as ichthulin, belongs to this category. 1 



1 From recent researches of Levene it appears that different forms of ichthulin 

 exist. The ichthulin of carp eggs thus yields a reducing substance on hydrolytic 

 decomposition, while that of the cod apparently contains no carbohydrate radicle. 

 The latter, on treating with alkalies, yields a paranucleinic acid, which is similar 

 to vitellinic acid (see below). Elementary analysis of the two forms has given the 

 following results: Ichthulin of carp eggs (Walter): 0,53.52; II, 7.6; N, 1 ">.'>,">; 

 S, 0.41 ; P, 0.43 ; Fe, 0.10 ; O, 22.lt) per cent. Ichthulin of codfish eggs : C, 52.44 ; 

 H, 7.45 ; X, 15.96 ; S, 0.92 ; P, 0.65 ; Fe and O, 22.58 per cent. 



