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ZOOLOGY: J. P. BAUMBERGER 
of water. The banana was thoroughly mashed before fermentation. 
This material was pressed through a sugar sack giving 1200 cc. of fluid. 
Medium A consisted of this fluid, diluted twice with enough pow- 
dered agar-agar added to make up to 1.5%, then boiled, poured into test 
tubes and plugged with nonabsorbent cotton and sterilized in the auto- 
clave for twenty minutes at 19 pounds pressure with vacuum at start. 
Medium C consisted of 12 grams yeast per 200 cc. tap water and 1.5% 
agar-agar. 
Medium D consisted of tap water and 1.5% agar-agar. 
Medium J consisted of grape sugar, cane sugar, ammonium tartrate, 
citric acid, K2HP04,MgS04,H20 (proportions as used by Loeb^), 1.5% 
agar-agar. This was sterilized three successive days in Arnold Sterilizer. 
The rates of development of larvae on these media were as follows: 
MEDIA 
A Aseptic fermented banana agar 
A Septic fermented banana agar. 
C Aseptic yeast agar 
D Aseptic agar 
D Septic agar 
J Aseptic synthetic medium 
J Septic synthetic medium 
Aseptic larvae on A developed at half of the rate of septic larvae on 
the same medium. The growth of these retarded individuals could be 
greatly accelerated by adding two loopfuls of septic A to their food. 
This was done in the case of larvae which in twenty-six days have only 
reached a length of 2.5 mm. After three days the larvae were 4 mm. 
long and had doubled in diameter; another millimeter was gained the 
next day and on the sixth day the larvae formed pupae from which 
large adults emerged. Since larvae grow more rapidly on abundant 
dead yeast (C) than on less abundant living yeast, the fungus is merely 
the food of the insect. 
It is apparent from the foregoing that the rate of growth is depend- 
ent on the abundance of yeast in the media. Dead yeast serves equally 
well in determining this rate. We may therefore conclude that yeast 
serves as food for Drosophila larvae. There is also evidence that other 
microorganisms may furnish nutrition for these flies. For example 
flies were reared from egg to adult on agar-agar (D) which had been 
contaminated by a living anaerobic bacterium as yet undetermined. 
After the initiation of these experiments I found that Delcourt and 
Guyenot^ and Guyenot^ had already shown that yeast and most bac- 
teria are of value to Drosophila larvae, especially when the larvae are 
28 From hatching to death 
12 From hatching to pupation 
9 From hatching to pupation 
5 From hatching to death 
26 From hatching to pupation 
5 From hatching to death 
10 From hatching to pupation 
