THE PHYSIOLOGY OF CELL-DIVISION 



VI. EHYTHMICAL CHANGES IN THE RESISTANCE OF THE DIVIDING 

 SEA-URCHIN EGG TO HYPOTONIC SEA WATER AND THEIR 

 PHYSIOLOGICAL SIGNIFICANCE 



RALPH S. LILUE 



Clark University, Worcester, Mass. 



INTRODUCTION 



In experiments performed at Woods Hole dm^ing the sum- 

 mer of 1901 Lyon^ found that dividing Arbacia eggs varied greatly 

 in their susceptibility to cyanide poisoning at different periods 

 of the cell-division cycle. Eggs placed in cyanide-containing 

 sea-water (m/100 to m 200 KCN) some time previously to 

 the first cleavage, but not too soon (later than 15 or 20 minutes) 

 after fertilization, withstood exposures of several hours without 

 losing the power of development; while eggs exposed to the same 

 solution at the time of cytoplasmic division were promptly 

 killed. After the completion of cleavage a return of resistance 

 was observed; this was followed by a second decline at the time 

 of the second cleavage. It has been shown by Loeb- that the 

 resistance to cyanide poisoning is much greater in the unfer- 

 tilized than in the fertilized egg; Lyon found that fertilization 

 is immediately succeeded by a period of high susceptibility, 

 lasting some ten or fifteen minutes; then follows a resistant 

 period which is terminated by the first cleavage. At first it 

 was uncertain whether the resistance reached its minimum 

 during or immediately after cleavage; Lyon inferred the latter, 

 and supposed that the cyanide acted by preventing the oxida- 

 tions necessary for the nuclear resynthesis following cytoplas- 

 mic division. A later examination of the question by Mathews^ 



' E. P. Lyon, Amer. Journ. Physiol., 1902, vol. 7, p. 56. 

 2 J. Loeb, Biochem. Zeitschr. 1906 vol. 1, p. 200. 

 ' A. P. Mathews, Biol. Bull., 1906, vol. 11, p. 137. 



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