THE PHYSIOLOGY OF CELL-DIVISION 701 
That the calcium prevents the rapid increase of permeability 
caused by the pure solution may readily be proved. I have 
already described experiments of this kind.’ Eggs placed in 
pure sodium iodide or sulphocyanate solutions lose pigment 
rapidly, in nitrate solution more slowly—within several minutes, 
—and still more slowly in solutions of the other sodium salts. 
Calcium-containing solutions of the same salts, in which the same 
quantities of eggs have been placed, remain uncolored for hours, 
or in the case of the more weakly active salts for a day or more. 
In the pure solutions eggs are rapidly killed,’ i.e., lose the power of 
developing on fertilization; in calecium-containing solutions, on 
the other hand, they preserve their normal properties for greatly 
prolonged periods, varying in duration with the salts, according 
to the specific toxicity of the latter. The rapid increase in per- 
meability is thus prevented at the same time as the toxic action 
is diminished; hence the preservation of the normal properties 
of the protoplasm, i.e., the antitoxic action exercised by calcium, 
appears to be dependent on the maintenance of a normal or 
approximately normal state of surface-permeability. The cleav- 
age-Initiating action, with which is also associated a rapid increase 
of permeability, is similarly prevented by the calcium. The 
inference that the increase of permeability is the essential or crit- 
ical change in normal or parthenogenetic fertilization thus seems 
highly probable. 
Several years ago Loeb discovered that while only a few eggs 
at best developed to a larval stage after simple membrane-forma- 
tion by fatty acid or otherwise—the great majority dying early 
—the proportion undergoing favorable development was greatly 
increased by subsequent treatment with hypertonic or cyanide- 
8’ American Journal of Physiology, 1911, vol. 27, p. 289. 
® Different eggs vary in their resistance to the destructive action of pure isotonic 
solutions of neutral alkali metal salts. Unfertilized Arbacia eggs may survive 
several hours immersion in isotonic NaCl solution; Asterias eggs are killed com- 
paratively rapidly, while Strongylocentrotus eggs may remain living in this solu- 
tion for 48 hours (ef. J. Loeb: Biochemische Zeitschrift, 1906, vol. 2, p. 84). 
The relative ease with which parthogenetic development may be induced corre- 
sponds to this difference. Strongylocentrotus eggs are the least responsive (Loeb: 
Chemische Entwicklungserregung, p. 67), Asterias the most. 
JOURNAL OF MORPHOLOGY, VOL. 22, No. 3 
