October 21, 1910] 



SCIENCE 



567 



be shown that only the yolk and pigment 

 granules break down. The oil is unaffected. 

 The eggs are first centrifuged and then cyto- 

 lyzed (with CHCI3 or saponin) or first cyto- 

 lyzed and then centrifuged. Swelling and 

 break down of the granules take place simul- 

 taneously and suddenly. It is impossible to 

 say which precedes and which follows. Many 

 eggs contain granules which do not break 

 down on cytolysis although the whole egg 

 swells so that it would appear as if the con- 

 nection of the granules in an egg with cytol- 

 ysis were purely secondary and that chloro- 

 form or saponin does not combine with them 

 and break them up. Clear fragments of eggs 

 cj^olyze as readily as granular fragments. 



This supposition is further supported by 

 the fact that the granules (excepting oil) of 

 Arbacia eggs are broken up into exactly the 

 same products characteristic of cytolysis 

 when the eggs are crushed in sea water. 

 There must be something in the egg in whose 

 presence the granules are stable or something 

 in the sea water in whose presence they are 

 unstable, and the egg surface forms an im- 

 penetrable barrier for this substance. The 

 latter alternative may be tested much more 

 easily experimentally and it appears probable 

 that the calcium salts of sea water are chiefly 

 responsible for the breakdown of the yolk and 

 pigment granules. If crushed in pure 0.6 m 

 KaCl or KCl the granules retain their color 

 and integrity. If cytolyzed in pure NaCl the 

 granules remain intact, although they are 

 changed in some way, for any dye or pigment 

 they may contain passes out of them. The 

 whole egg nevertheless swells. The cytolysis 

 of the sea-urchin egg would be in all respects 

 like that of the. annelid were it not for the 

 calcium of the sea water. The yolk granules 

 of annelid eggs are stable in sea water. 



The relation of calcium to cytolysis shows 

 further that it is not present in the egg iu the 

 same condition as in the sea water and does 

 not pass into the egg in that condition unless 

 its surface has been destroj-ed by some cyto- 

 lytic substance. 



The conception of cytolysis to which I have 



been led is essentially that of Hamburger, 

 Koeppe and other physiologists. It is certain 

 that during cytolysis there is a progressive 

 change from impermeability to complete per- 

 meability for most diffusible substances, for 

 it is a change from a definite plasma mem- 

 brane to no true surface whatsoever, if the 

 eggs remain in the solution long enough. 

 The apparent surface of cytolyzed eggs is 

 merely the artificial fertilization membrane 

 formed in the first stages of cytolysis. The 

 permeability of the plasma membrane is in- 

 creased to a certain extent and under these 

 conditions substances pass out which form 

 an albuminoid membrane. In the next stage 

 the egg becomes permeable to the salts of sea 

 water when swelling of the egg and disintegra- 

 tion of the granules takes place, and at the 

 same time the egg surface loses its continu- 

 ity. 



The cause of the swelling is simply the sub- 

 stitution of a surface freely permeable to salts 

 for one quite impermeable to them. In the 

 normal egg the sum of the osmotic pressures 

 of the substances within the egg just counter- 

 balances that of the salts of sea water. This 

 does not mean that the substances within the 

 egg are the same as those without. The egg 

 is not a mass of proteid saturated with sea 

 water, but even its salt content is different. 

 Suppose the membrane separating these two 

 phases becomes permeable for the dissolved 

 substances of one phase but not for those of 

 the other. The result is the same as placing 

 the cell in distilled water. It swells until its 

 turgor pressure is balanced by the tension of 

 its artificial membrane. 



The slowness with which eggs swell when 

 placed in distilled water, considering the 

 large surface area, points to the view that 

 even water encounters resistance in its exit 

 from and entrance into the egg. In distiUed 

 water the egg slowly swells to a certain size, 

 at which point it suddenly swells and a deli- 

 cate membrane forms. I am inclined to be- 

 lieve that at this point the surface becomes 

 freely permeable to the entrance of water and 

 the whole egg swells (within the artificial 



