THE REPRODUCTIVE GLANDS. 449 



To isolate the euglobulin from the total globulin fraction, this is 

 repeatedly washed with a one-half saturated solution of ammonium 

 sulphate (by centrifugation) until the salt solution no longer gives 

 the biuret reaction. The euglobulin is finally collected on a filter, 

 coagulated in the drying-oven at 100 C., and washed with hot 

 distilled water until free from salts. 



Ovomucoid. The mucoid substance which can be isolated from 

 the albumen of hens' eggs is present in considerable amount, consti- 

 tuting about 10 per cent, of the total solids. Elementary analysis 

 of ovomucoid has given the following results : C = 48.82, H = 

 6.96, N =12.51, 8 = 2.19. The greater part of the sulphur (not 

 less than three-fourths) is present in loosely combined form. On 

 boiling with dilute mineral acids it yields a reducing substance 

 glucosamin. A chondroitin-sulphuric acid complex is not present 

 in the ovomucoid molecule. 



According to most authors, the ovomucoid does not give the 

 Adamkiewicz reaction, while Langstein states that in the case of 

 his own preparations he always obtained a positive result. He 

 suggests that the negative findings of others may have been refera- 

 ble to the possible absence of glyoxylic acid in the glacial acetic 

 acid employed. 



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 dry- 

 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 white yolk. 

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

 riphery of the yolk, immediately beneath the vitelline membrane. 



29 



