NUTRITION 87 



phila) can complete its larval stage in a solution of cane sugar 

 and salts adsorbed in filter paper. The lar/ae grows quickly, 

 and on addition of ammonium tartrate, glucose, and citric 

 acid, successive generations can be reared. Here at first 

 sight appears to be an organism that can flourish in a medium 

 deficient in nitrogen compounds of the degree of complexity 

 hitherto thought to be required by animals invariably. This, 

 however, is not the case. 



The nitrogen supply of Drosophila has been made the 

 subject of recent investigation by Baumberger (1918). The 

 alimentary tract in Drosophila larvae teems with yeasts. In 

 order to explore a possible relation between the yeast organisms 

 and the nutritional processes of the fly, Baumberger steri- 

 lised eggs and pupae by immersion for a short period in 85 per 

 cent, alcohol. Sterile individuals having been so obtained, 

 both sterile and normal individuals were placed on (a) sterile 

 banana— agar culture media, and (b) a sterile synthetic medium 

 containing mineral salts, sugar, and ammonium tartarate as 

 the sole source of nitrogen. The consequences of this treat- 

 ment on the two classes of individuals w^re striking. Normal 

 {i.e. unsterilised) individuals deposited eggs which grew into 

 larvae that pupated normally on both banana-agar and synthetic 

 media. The larvae which developed from sterilised eggs and 

 as the offspring of sterilised pupae failed either to grow or 

 pupate on a sterile medium of either type ; they only survived 

 a few days. When, on the other hand, similar sterilised 

 individuals were placed on media of the same nature which 

 had been previously infected with yeasts, they at once began 

 to thrive, pupating as usual. Thus in the presence of yeasts 

 Drosophila can grow on an artificial medium with ammonium 

 tartarate as its only source of nitrogen. 



It may now be asked whether the food requirements are 

 met by any by-products of fermentation. This Baumberger 

 tested by boiling the yeast before adding it to the sterile cul- 

 tures ; fermentation was in this way prevented. The larvae, 

 however, grew steadily, and the possibility that the fly larva 

 actually ingests the yeasts alone remained. On cultures of 

 compressed yeast-agar with yeast nucleo-proteins as the sole 



