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Direct microinjection of substances in penetration-sensitive embryos.

We have modified an electrode holder into an oil-pressure holder by fitting an internal platinum heating filament into the holder. This design enables easy preparation, mounting, and exchange of micropipettes. Micropipettes with very thin tips (outer diameter less than 0.1 micron) can be used, as the system allows the use of back-filled pipettes. Therefore, successful microinjections in penetration-sensitive embryos are possible. The characteristics of the system are described, and its advantages and disadvantages, as compared to other microinjection systems, are discussed.