SUSCEPTIBLE AND RESISTANT PHASES OF THE DI- 
VIDING SEA-URCHIN EGG WHEN SUBJECTED TO 
VARIOUS CONCENTRATIONS OF LIPOID-SOL- 
UBLE SUBSTANCES, ESPECIALLY THE 
HIGHER ALCOHOLS* 
FRANCIS MARSH BALDWIN 
INTRODUCTION 
That dividing Arbacia eggs show periods of varying suscepti- 
bility and resistance when exposed to chemical substances and to 
various physical conditions has been proved by numerous inves- 
tigations. When eggs from a single fertilized lot were placed at 
regular successive intervals after fertilization in cyanide contain- 
ing sea- water (m/lOO to m/200), Lyon ^ found that they were 
highly resistant to poisoning fifteen or twenty minutes after 
fertilization, while eggs exposed to the same solution at the time 
of cytoplasmic division were promptly killed. Later, after the 
first division had been completed, the resistance to poisoning 
again returned, followed by a second susceptible period at the 
second cleavage. Loeb ^ later noted that the unfertilized eggs show 
greater resistance to cyanide poisoning than the fertilized eggs, 
and Mathews ^ indicated that in dividing eggs, the period of max- 
imum susceptibility is “immediately before and during segmenta- 
tion,’' and that just after segmentation the egg becomes relatively 
highly resistant. Similar results were obtained by Spaulding ^ 
in experiments with weak solutions of ether (1/64 per cent in 
sea-water). The period of high resistance continued up to the 
beginning of the first cleavage, and then fell during cleavage to 
zero, with a sharp rise immediately afterwards. There was a 
short period of susceptibility immediately following fertilization. 
He found also in acid and salt solutions (pure isotonic KCL and 
NaCL) a similar but less clearly defined rhythm of susceptibility. 
Eggs subjected to heat, electrical stimulation and hypertonic 
sea-water behave in a similar manner. Thus, Lyon ® observed that 
the eggs were most resistant to heat at a time previous to the first 
cleavage, and were most readily injured at the time of division. 
* From the Marine Biological laboratory, Woods Hole, Mass., and the Department 
o£ Zoology, Iowa State College, Ames, Iowa. 
