28o THE UNFERTILISED EGG AS A [pt. iii 



trustworthy, but not for combined sugar, in view of the demonstra- 

 tion of Holden that all copper-reducing methods are seriously inter- 

 fered with by the presence of amino-acids and protein breakdown 

 products. No method at present in use gives satisfactory results in 

 those conditions, but the most reliable is that of Hagedorn & 

 Jensen. No estimations of total carbohydrate in egg-white alone at 

 present exist, but there is a single figure for glycogen due to Sakuragi. 

 Morner found no evidence of fructose, pentoses or maltose. 



A curious phenomenon : the fluorescence of egg-white has been 

 reported by van Waegeningh & Heesterman, but it only occurs if 

 the egg is not perfectly fresh, and is therefore probably not physio- 

 logical. 



I '7. The Avian Yolk 



The vitelline membrane was investigated by Liebermann in il 

 who found that it consisted almost exclusively of keratin. This he 

 purified, and, having freed it from ash, made an elementary analysis 

 of it, which is shown in Table loa. Some experiments which demon- 

 strate the peculiarities of the vitelline membrane have been devised 

 by Osborne & Kincaid. They found that a fresh yolk floated into 

 distilled water, o-g per cent. NaCl solution, or glycerol, behaved 

 exactly like a red blood corpuscle in that it swelled up and burst 

 in the former, and shrank to a corrugated globe in the latter, while 

 in the isotonic salt solution it remained unchanged. But with other 

 treatment, nothing took place which corresponded to haemolysis. If 

 the yolk was put into lo per cent. NaCl solution, it did not shrink, 

 as had been expected, but swelled up, owing to the penetration of 

 the saline and the consequent osmotic pressure due to the dissolving 

 of the vitellin in the saline. This showed at once the scleroprotein 

 nature of the membrane and its impermeability to vitellin even when 

 in solution. The membrane is also impermeable to phosphatides and 

 fats dissolved in ether, for if a yolk is put into ether it sinks and swells, 

 so that the upper pole is distended by an accumulation of deeply 

 pigmented ether. But until the yolk bursts, as it eventually does, 

 not a trace of pigment or other substance passes out into the ether, 

 and the same results were found with chloroform and carbon disul- 

 phide. In alcohol, on the other hand, there is no swelling, for the 

 alcoholic solution of phosphatides and other bodies can pass out 



