The banana has been studied as food for the rat by Benedict and Sugiura (32) and as a nutrient substance for the banana fly, Drosophila ampelophila, by Loeb and North-rup (33). The former investigators found it deficient in protein, and in water-soluble B. This last observation is remarkable since banana constituted about 80 per cent of their experimental diet. Their studies also seem to verify the generalization of Steenbock and Gross (28) that this yellow fruit contains more fat-soluble A than do fruits in general, or more than the roots and tubers not so pigmented. Benedict and Sugiura also stated that in their experience casein proved a much more effective supplement to the banana than washed and dialyzed beef. In their experiments the banana supplemented with casein, and a source of water-soluble B (yeast or carrot extract) proved inadequate for the production of milk by lactating rats. The failure lay in the quality of the milk and not in the quantity, since the mothers failed to succeed with both small and large litters.

Loeb and Northrup found sterile banana inadequate for the nutrition of the banana fly, but banana cultured with yeast was satisfactory (33). The interpretation placed upon this observation is that the yeast cell produces synthetically some substance or substances, not present in the banana, but necessary for the nutrition of the fly. The nature of this relationship between the development of yeast and the improvement of the nutrition of this insect is not clear.