290 
IOWA ACADEMY OF SCIENCE Vor,. XXVII, 1920 
merits the opposite procedure was adopted, that is, the time was 
varied and the concentration kept constant. 
Practically the same procedure was observed throughout the 
entire experimentation. At each of the successive intervals after 
fertilization, usually ten minute intervals, about one-half of a 
medicine pipette containing a suspension of the inseminated eggs 
was placed in a small corked Erlemyer flask, contining 50 c.c. 
of the solution of the alcohol in sea-water, and allowed to remain 
for the time of exposure chosen (usually five minutes). After 
the given time had nearly elapsed, the excess liquid was poured 
off, and the eggs with a little of the liquid were placed in a watch 
glass and the immediate results of the treatment were observed 
under the low power of the microscope. At the termination of 
the time of exposure, the watch glass containing the eggs was care- 
fully immersed in a large volume of sea-water in a finger bowl 
and the water was changed several times to rid it of the excess 
substance. Finally the eggs were very carefully washed with a 
stream of water from the medicine-dropper, and set aside to under- 
go development. The proportion proceeding with development 
to the free-swimming larval stage was subsequently determined. 
It was found that the estimate of the proportion surviving to the 
blastula stage was more readily and exactly made if the watch 
glass containing the eggs was removed from the bowl of sea-water 
just before the free-swimming larval stage was reached. Thus 
all survivors could be confined within a small volume, and the 
count or estimate easily made. As a rule, the experiments were 
carried up only to about the time of second cleavage, since the 
evidence indicates that the same variation of susceptibility occurs 
in each cell division cycle. Moreover divergencies between the 
different eggs in any lot become more pronounced as time elapses, 
and it is important that all eggs of a lot should be in the same 
physiological state at the time of treatment. 
At first several preliminary experiments were necessary in 
order to determine the most suitable range of concentrations to 
be used, since the times of exposure determined upon were brief, 
the longest being ten minutes, while in some cases the exposure 
was only three minutes. In this connection, the tables given by 
Lillie in his paper on the action of various anaesthetics in sup- 
pressing cell-division in sea-urchin eggs, were exceedingly helpful. 
For i-amyl^^ alcohol, he finds 0.45 to 0.4 volumes per cent a 
favorable anaesthetic concentration for eggs subjected for two and 
one-half hours, while 0.5 vol. per cent and above are somewhat 
