578 STUDIES IN GENERAL PHYSIOLOGY 



experiments in order to find out whether there was a division 

 of the nucleus without a segmentation of the protoplasm, 

 and whether this division was mitotic. Norman found that 

 by carefully selecting the concentration of the sea- water a 

 division of the nucleus without a segmentation of the proto- 

 plasm occurred, and, moreover, that the division was mitotic. 1 

 The number of cells into which the egg divides at once when 

 brought back into normal sea-water is often larger than the 

 number of the nuclei preformed in the concentrated sea- 

 water. It therefore seems as if a further division of the 

 nuclear matter occurs immediately after the eggs are put 

 back into normal sea- water. The addition of sodium chlo- 

 ride seemed to injure the eggs, and I asked Mr. Norman to 

 try the effects of other chlorides. He found that an increase 

 in the concentration of sea- water by the addition of MgCl 2 

 is less harmful than that of any other chloride. 



It seems to me that it is necessary to discriminate in these 

 experiments between two different effects produced by the 

 addition of salts (or the increase of the concentration of sea- 

 water). The one effect is that produced on the nucleus and 

 consists of a destruction (liquefaction?) of the nuclear mem- 

 brane, and possibly a dissolution of the substance which 

 binds the chromosomes together. This effect seems within 

 certain limits to increase with the concentration of the sea- 

 water. The other effect consists in the gradual suppression 

 of the motility of the protoplasm. This may possibly be 

 due to a decrease in the fluidity of the protoplasm (water 

 rigor). This effect also becomes stronger with the increase 

 in the concentration of the sea-water. At a certain point in 

 the increase of the concentration the nuclear membrane will 

 be dissolved and the chromosomes scattered (through proto- 

 plasmic motions), while the protoplasm is no longer able to 

 undergo segmentation. This was observed by Norman. If 



i W. W. NORMAN, Archivfiir Entwickelungsmechanik, Vol. Ill (1896), p. 106. 



