374 EALPH S. LILLIE 



EXPERIMENTAL 



When placed in dilute sea-water Arbacia eggs take up water 

 osmotically and swell; the rate of this change varies with the 

 dilution of the medium and with the condition of the eggs, and 

 is surprisingly slow in unfertilized eggs.^^ If the dilution is 

 sufficient the eggs eventually undergo a disruption or cytolysis, 

 due to the destruction of the normal semi-permeable properties 

 of the plasma-membrane. The pigment then leaves the eggs 

 and colors the water; the cell-contents turn a characteristic 

 pink, and the protoplasm assumes a granular appearance. This 

 form of cytolysis has definite and unmistakable characteristics. 



Osmotic distention in dilute sea water is destructive to the 

 egg only if it exceeds a critical limit, which appears to be deter- 

 mined by the properties of the plasma-membrane. The latter 

 may undergo a certain increase in area without losing the nor- 

 mal semi-permeability; such a partly swollen egg on return to 

 normal sea-water loses the excess of water, and if previously 

 feitilized continues development;^^ or if unfertilized it may be 

 fertilized and will then develop. A considerable addition to 

 the normal water-content of the protoplasm may thus be made 

 without permanent injuiy; this possible addition is greater in 

 the case of the fertilized than of the unfertilized egg. Analo- 

 gous conditions are found in other cells; the variations in the 

 resistance of homologous cells from different animals are espe- 

 cially interesting in this relation, since some evidence exists that 

 these variations are correlated with definite differences of lipo id- 

 content. According to Hober the red corpuscles of the horse 

 first begin to lose haemoglobin in a NaCl solution of 0.68 per 

 cent concentration; for the ox the coriesponding limiting con- 

 centration is 0.58 per cent, for man 0.45 per cent.-" Obviously 

 these differences are not due to differences in the os- 

 motic pressure of the cell-contents, since the plasma has the 

 same freezing point in all cases. For some special reason the 

 corpuscles require greater osmotic distention in some animals 



1* Cf. my paper just cited, p. 256. 



1' See table 5, p. 384. 



20 Physikalische Chemie der Zelle und der Gewebe, 4th Edition, 1914, p. 77. 



