1. A technique is described for the culture of germ-free Drosophila adults on defined diets. The complete larval diet, with the agar base replaced by cotton-wool, was found to be adequate for adults and permitted them to lay more or less normal numbers of eggs during a 16-day test period.

2. Omission tests showed that casein, the B vitamins (other than B12 and biotin) K and Mg were essential for normal ovary development.

3. Casein could be replaced with an amino acid mixture. The ten ‘essential’ amino acids were all found necessary for egg production but arginine, histidine and methionine were apparently synthesized, although at an inadequate rate. The remaining essential amino acids seemed to be the nutrients required in the greatest amounts since egg production stopped soonest when they were omitted. Individual ‘nonessential’ amino acids could be removed from the mixture, but a supply of them was necessary for normal egg production and viability.

4. Omission of fructose lowers egg production but does not cause its cessation even after 16 days.

5. The difficulty of determining that essential supplies are not being met by contaminants is illustrated by examination of cholesterol requirements. In this case, and possibly also for choline, the requirement for egg formation is very much less than for larval development, and might be satisfied from contamination of the medium constituents.

6. Neglecting these trace supplies (which can be measured only in fractions of a microgram per 5 ml. medium) RNA, choline, cholesterol and biotin seem unnecessary for egg formation. The quantitative requirements of the normal adult female must therefore be different from those of the larva.

7. It was not possible to produce a true P deficiency, or to be certain that traces of Ca and Cl in the medium were not sufficient to permit normal fecundity.

8. The ovary is shown to be capable of recovery from protein starvation and to respond to omission of single essential amino acids by ceasing to form new chambers. The majority of deficiencies result in inhibition of vitellogenesis, after a period when inviable eggs are laid. Only Mg and pyridoxine omission produced distinguishable pathological changes, which are illustrated.

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