130 FRANCIS MARSH BALDWIN. 



In the controls about one half of the eggs were in the two- 

 celled stage at fifty-three minutes after fertilization, and at 

 sixty-five minutes between 85 and 90 per cent, were divided. 

 There is a definite period of well-marked susceptibility imme- 

 diately following fertilization; the susceptibility then gradually 

 and progressively declines up to the end of forty-eight minutes 

 (just before the first cleavage). There then follows a very sus- 

 ceptible period just at the time of cleavage. Later the resistant 

 phase reappears until about the time of second cleavage. If 

 the time intervals are plotted as abscissae, and the percentage of 

 surviving blastulae as ordinates, the relationships may be repre- 

 sented in the curve shown in Fig. I. 



HEXYL ALCOHOL. 



In exploring the range of suitable concentrations for hexyl 

 alcohol, the next higher member of the series, assuming that it 

 should be approximately three times as effective as i-amyl alcohol, 

 three preliminary experiments were performed. For these, solu- 

 tions of o.i, 0.25 and 0.30 vol. per cent, were used respectively. 

 The time of exposure was shortened to five minutes, for the 

 reason that it was thought the concentrations were, if anything, 

 a little above the optimum. The results clearly showed that 

 the solutions of o.i vol. per cent, was not sufficiently toxic to 

 demonstrate any variation of susceptibility in the eggs, since at 

 whatever period they were exposed practically all eggs survived 

 to the free-swimming blastula stage. On the other hand, the 

 two higher concentrations proved too toxic, so that practically 

 none of the eggs continued their development after subjection 

 to these solutions at any period. The 0.25 vol. per cent, solution, 

 although it suppressed further development, was not quite 

 intense enough in its action to cause cytolysis in the eggs, with 

 few exceptions. The 0.30 vol. per cent, concentration caused 

 very evident cytolysis, and rupture was almost universal. 

 Accordingly, series of experiments were carried out to test the 

 various concentrations between o.i vol. per cent, and 0.25 vol. 

 per cent. Two of these experiments are summarized in Table II., 

 and may be regarded as typical. 



These results show a much less definite evidence of a rhythm of 



