Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

7.2
untreated embryos showed almost as hÌgh an incidence of deaths and malformations
as windowed and treated embryos. l,loreover the defects produced
lnvolved predomlnantly the central nervous system.
4.2.2 Standard Techn îc
From thîs observation a standard experimental method was developed
which produced a high incídence of open neural defects. Each egg wíth
an embryo of medlum-size on candl ing at 26 to 30 hours of incubation
was wiped wíth a gauze square of 702 alcohol and cuts made in the shell.
During the operation the egg was held obliquely to avoid damaging the
embryo, and the shell membrane careful ly preserved. A short cut was
made over the air cell and a 1.0 cm. x 1.5 cm. hexagonal or rectangular
window made over the embryo. The egg was cleaned with 7Oy" alcohol and
transferred to a holder in tlre experimental cabinet, with the shell
window uppermost. The shelI membrane was then punctured gently with
sterile forceps, first over the air cell and then over the-embryo, allowíng
air to be drawn into the egg with col lapse of the air cell. 2 ml . of
albumen were then carefulìy withdrawn with a sterile syringe and widebore
unpoînted needle. E99s in which the vitelline membrane was damaged or
those where the embryo was not îmmediately beneath the shell window were
rej ected .
By this means embryos of quite a narrow range of developmenial stages
were exposed to the act¡on of an artíficial. air space, with no protect¡on
from an overlying layer of albumen but Iittle distortion from excessive
f latteníng or stretching.
\.2.3 Examinatíon of Embryo.s
As each blastoderm was fully exposed by this technic of windowing,
It was lnspected and its diameter measured 1n nillimeters with a plast¡c