STUDIES WITH THE CENTRIFUGE 35 



Evidence for a substance unaffected by centrifuging 



When the egg is centrifuged the yolk spheres are driven into 

 one hemisphere with no visible substance between them. Never- 

 theless the fact that, when so driven, the globules maintain their 

 spherical form and neither resume the appearance which they 

 have in the yolk glands of the parent nor resemble the mass of 

 yolk granules set free when the egg is crushed, indicates that the 

 clear spaces between the globules in the yolk hemisphere of the 

 centrifuged egg contains an unstained ground substance of some 

 sort, which is not separated by centrifuging. In partially cen- 

 trifuged eggs a few purple granules still remain in the spaces 

 between the yolk globules. Moreover, without admitting the 

 presence of some substance other than yolk in the centrifugal 

 hemisphere we could not account for the normal division, since 

 a concentration of yolk in one part of an egg usually interferes 

 with or even inhibits cleavage in that part. Cyclops, with its 

 large yolk spheres, has shown better than any other eggs that the 

 purple granules may be entirely pushed out of the centrifugal 

 hemisphere, leaving colorless spaces between the globules of yolk; 

 and that these spaces contain enough of the essential protoplasm 

 to make normal cell division possible. If a colorless ground sub- 

 stance does exist we should expect to find that the acid and basic 

 "granules" are really granular inclusions and not artifacts. 



The frog's egg when centrifuged at about the same speed as , 

 that used for cyclops fails to segment in the yolk hemisphere. 

 The frog's egg, however, has its yolk largely in one hemisphere 

 in the normal condition, so that the result of a given speed of the 

 centrifuge is probably equal to the effect of a much stronger force 

 applied to cyclops or sea urchin eggs where the materials are uni- 

 formly distributed. If we centrifuged cyclops or the sea urchin 

 sufficiently hard I believe it very likely that we could drive the 

 yolk so completely to the centrifugal pole that the ground sub- 

 stance would be entirely pushed out from between the globules 

 and a result comparable to that in the frog would be obtained. 

 The yolk- and the granule-containing alveoli probably move 



