CHAPTER 18 



Breaking of the Egg 

 Egg Fractions and Contents 



When centrifuged with low forces, 3000 X g for two minutes, the eggs 

 remain spherical but become stratified. When centrifuged at 10,000 X g 

 for four minutes, most batches of eggs stratify, become dumbbell- 

 shaped and then break across the yolk into two slightly unequal spheres 

 or "half-eggs" (Plate VII and Fig. 12). In the centrifuge tubes (Photo- 

 graph 10) there are three distinct layers, the white half-eggs toward 

 the top (centripetal end) of the tube, a pinkish layer of elongate un- 

 broken eggs a little below, and a layer of red half-eggs at or near the 

 bottom (centrifugal end) of the tube. In some cases there are five 

 layers with this force due to the breaking of the red half-eggs into 

 quarters. The layers now are: white half-eggs at the centripetal pole, 

 unbroken whole eggs, yolk quarters, unbroken red halves, and pig- 

 ment quarters at the centrifugal pole (E. B. Harvey, 1936, photo 6). 



These quarters can also be obtained by recentrifuging the red halves. 

 The white half-eggs may also be broken into clear and mitochondrial 

 quarters by pipetting them off and recentrifuging them in a slightly 

 less dense sugar solution for about 45 minutes. The nucleus is always 

 in the white half-egg and in the clear quarter-egg. It is lighter than 

 the granules and always lies just under the oil cap at the centripetal 

 pole. 



The white halves contain oil cap, nucleus, clear layer, mitochondria, 

 and a little yolk; the slightly smaller red half contains most of the yolk 

 and all the pigment granules; the clear quarter contains oil cap, 

 nucleus, and clear layer; the mitochondrial quarter contains all the 

 mitochondria and some yolk; the yolk quarter contains only yolk and 

 the pigment quarter, all the pigment granules, and a little yolk. 



The sizes of the fractions obtained with a force of 10,000 X g are 

 given in Table 9; Photographs 1-9, Plate VII, and a chart drawn from 

 the photographs in Figure 12 (E. B. Harvey, 1932, 1936, 1940c, 1951). 



Although the size of the fractions obtained by centrifuging at 10,000 

 times g for 4 minutes is usually as given, there do occur batches of 



