730 STUDIES IN GENERAL PHYSIOLOGY 
alive for several days until they finally become the prey of 
bacteria; while the mature eggs become opaque and die in 
from four to twelve hours after maturation has been com- 
pleted. 
Is the death of the mature but undeveloped egg brought 
about through internal conditions, or through the bacteria 
contained in the sea-water ? 
A trustworthy way of determining this consists in making 
sterile culture of the eggs in sea-water. This is a relatively 
simple procedure in the case of starfish. Hight flasks were 
sterilized, filled with sterilized sea-water, and again heated 
for twenty minutes on three successive days to 100°C. A 
female starfish was thoroughly washed externally, an arm 
was opened, and one of the ovaries removed with sterilized 
forceps and placed in sterilized sea-water. From the thick 
stream of eggs which at once flowed out of the ovary, a few 
drops were quickly introduced with a sterilized pipette into 
each of the sterilized flasks. A second series of eight flasks 
contained normal, unsterilized sea-water, and a fewdrops of the 
same eggs were introduced into these flasksalso. A third series 
of flasks were filled with sea-water, to each of which were 
added 2 c.c. of a putrid, foul-smelling culture of old starfish 
eggs in order to bring about a rapid development of bacteria 
from the beginning. Each of these flasks also contained 
eggs from the same culture as those in the sterilized flasks. 
That perfect sterilization had been attained in the first 
eight flasks was proved by the fact that all the flasks remained 
absolutely clear and cloudless during the course of the experi- 
ment, and that three of the flasks which had not been opened 
are even today (after six weeks) absolutely clear, and every 
egg can be individually recognized. The flasks containing 
the unsterilized sea-water became cloudy within as short a 
time as twenty-four hours, and after two days the eggs had 
become the prey of bacteria and no individual egg could be 
Digitized by Microsoft® 
