38 J. PERCY BAUMBERGER 



that were sterile or with which only a single species of microor- 

 ganism was associated. This was accomplished by means of an 

 ingenious method for the aseptic transfer of adults from one flask 

 to another and by the use of various media adverse to different 

 species of molds and bacteria. This method of sterilizing the 

 larvae is much less direct and requires more time than my 

 method of sterilizing pupae with alcohol. The flies were finally 

 found to be sterile except for the presence of yeast cells and these 

 were eliminated by a rapid transfer of females from bottle to 

 bottle, thus permitting aseptic oviposition in a few cases. The 

 sterile larvae which emerged were then fed on a medium of potato 

 and dead baker's yeast or dead baker's yeast, water, and cotton. 

 The authors at this time made no definite statement about the 

 function of the microorganisms, but left that for later papers. 

 In 1913 (a) Guyenot reported that he had been able to raise 

 fourteen generations of Drosophila in the absence of living organ- 

 isms. The larvae were reared equally well on potato and living 

 yeast, potato and dead yeast, and on dead yeast alone, but did 

 not grow normally on sterile potato. Guyenot ('13 b) there- 

 fore concluded that in nature the larvae nourish themselves 

 principally on hving yeast and other microorganisms. 



The work of Delcourt and Guyenot was unknown to me until 

 after I arrived at similar conclusions^^ by different methods. The 

 experiments with Drosophila as reported above are therefore in 

 part an independent corroboration of the work of these authors. 



Loeb ('15) reared Drosophila on a medium of salts and sugars 

 with ammonium tartrate as the only source of nitrogen and there- 

 fore concluded that this insect has as great synthetic power as 

 bacteria. Later ('16) he pointed out that yeasts may have been 

 intermediate in the synthesis of protein, and in a third paper 

 (Loeb and Northrop, '16 b) showed that yeasts serve as food for 

 Drosophila and are required for the growth of the larvae. ^^ 

 These authors were unable to isolate the substance in the yeast 



1^ My experiments extended over the entire period between May 1, 1916, and 

 June 1, 1917, and were partially published in three papers (see Bibliography). 



18 Eggs were sterilized by washing in 0.1 per cent HgClz for six to seven 

 minutes. 



