THE DIVIDING SEA-URCHIN' EGG 
291 
rapidly toxic. For capryl alcohol he finds the anaesthetizing 
concentrations to range between 0.012 and 0.02, and notes that 
even in sub-anaesthetic concentrations this alcohol exhibits a rel- 
atively high specific toxicity. With the help of these data, and 
also Fiihner's observations showing that in a series of mono- 
hydric aliphatic alcohols each member of the group is from three 
to four times as effective (for equimolecular concentrations) as 
its immediate predecessor, it became a comparatively easy matter 
to approximate the most suitable concentration of each alcohol 
after the first had been determined.^® 
AMYL ALCOHOL 
Summarizing briefly the results of preliminary observations: 
it was found that the most satisfactory concentration of i-amyl 
alcohol when used with exposures of three to eight minutes, was 
between 0.7 and 0.9 vol. per cent. Solutions of this strength 
are sufficiently toxic to prevent many but not all the eggs thus 
treated from developing to a larval stage. Solutions weaker than 
0.7 voL per cent permit practically all eggs to proceed to the 
blastula stage with those exposures, with little appreciable differ- 
ence. At 1.0 vol. per cent not more than 20 per cent of eggs 
form free-swimming blastul« even when expos*ed at the period 
of highest resistance; {e.g.^ 30 to 40 minutes after fertilization) 
and above this concentration the toxicity is such that the decline 
in survivals is very rapid. In 1.25 vol. per cent solutions, all eggs 
are killed in all stages with exposures of nine minutes. 
Table I summarizes the results of a typical series of experiments 
with i-amyl alcohol. This particular series of experiments was 
started in the afternoon of July 16, and the observations noted 
in the third column were carried over into the morning of the 
following day. A similar series of experiments performed at 
about the same time with the same alcohol in somewhat lower con- 
centration (0.8 vol. per cent), but with slightly longer (10 min- 
ute) exposures yielded substantially the same results. On the 
following day experiments were carried out on eggs subjected 
to 1.1 vol. per cent solutions with only brief (3, 4 and 5 minute) 
exposures with results noted above. 
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 immediately fol- 
lowing fertilization ; the susceptibility then gradually and progres- 
