354 THE FLUIDS OF THE EGG. 



readily be obtained in any considerable numbers, tbose of tbe 

 hen and of the carp are almost the only ones which have hitherto 

 been examined. Since, according to Gobley's investigations,* the 

 constituents of the eggs of both classes of animals are almost 

 perfectly identical, we may assume that an inference may with 

 some justice be drawn as to the composition of the eggs of all 

 other animals from that of the hen's egg. 



It is well known that the eggs of most animals do not contain 

 the same albuminous investment as bird's eggs, but simply a fluid 

 corresponding to the yolk, and enclosed by a membrane. We 

 will, therefore, begin by considering the yolk, the constitution of 

 which we only know from our experiments on that of the hen's 

 egg. The yolk of the hen's egg consists of a very viscid, thick, 

 scarcely translucent fluid, which is either of a yellowish red or of a 

 sulphur-yellow colour, devoid of odour, and of a faint but peculiar 

 taste. When mixed with water it forms a white, emulsive fluid, 

 imparts a blue colour to reddened litmus paper, and solidifies on 

 boiling into a very friable mass. It coagulates in cold alcohol, and 

 yields when shaken with ether a reddish or amber-coloured fat, 

 whilst a viscid white mass separates. 



On examining the yolk under the microscope, we find that it 

 consists of a semi-fluid mass composed of very fine granules (whose 

 diameters are too small to admit of being measured), amongst 

 which there swim variously sized yolk-corpuscles and fat-ylobules. 

 The latter are distinguished by a less intense yellow colour, and by 

 being covered with a layer of fine granules, whilst the yolk- 

 corpuscles are surrounded by a membrane, which is, as it were, strewn 

 with granules. W T hen the yolk is acted upon under the microscope 

 by hydrochlorate of ammonia, or other neutral alkaline salts, the 

 granules almost wholly disappear, leaving only shining and sharply 

 defined fat-globules, together with the somewhat distorted, oval, 

 fusiform, or cucumber-like yolk-cells. The latter also exhibit a 

 very faintly granular investing membrane. A similar distortion of 

 the yolk-cells may be produced by dilute acetic acid, but this does 

 not dissolve the suspended matter. But if the yolk be acted upon 

 by concentrated acetic acid or a dilute solution of potash, the 

 membranes of the yolk-globules likewise disappear, whilst a very 

 finely granular substance alone remains visible, together with 

 yellow-coloured fat. The yolk-globules behave, therefore, pre- 

 cisely the same as the milk-globules (see vol. i., p. 384), the only 



* Compt. rend., T. 21, p. 766 769; Journ. de Pharm. et de Chira., 3me 

 Ser., T. 11, p. 409417, et T. 12, p. 513; Journ.de Chim. He'd. T. 6, pp. 

 6769. 



