ZOOLOGY: J. P. BAUMBERGER 
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in large numbers. These investigators finally obtained aseptic flies 
by the use of media unfavorable to the different forms of bacteria. 
Yeast persisted longest but was finally eliminated by using food con- 
sisting of sterile yeast, water and cotton. Potato media were occasion- 
ally intercalated in the series as a test of the absence of living yeast 
cells. The transference of flies was made aseptically by the use of an 
ingenious suction apparatus. However, females from stock which 
had been ^aseptic' for several generations occasionally deposited sep- 
tic eggs and died in the center of a yeast colony. It is possible that 
living yeast was constantly present and that usually an insuflicient 
number of cells was carried to the potato medium. In such a case due 
to the absence of bios,^* growth would not take place. Guyenot 
later^^ reported that he had been able to raise Drosophila on sterile 
(unfermented) potato, but the percentage of larvae that pupated was 
small. Salomon^^ j^^g described the use of yeast as a food for man and 
a considerable literature deals with its use as food for farm animals. 
Schultze^^ has suggested that Drosophila larvae may feed upon bac- 
teria and yeasts in strange media such as sap, feces, formol, tumors, 
etc., from which the fly has been recorded. Henneberg^'* believes that 
these larvae feed upon microorganisms at the surface of vinegar. 
It is probable that the food relations pointed out in my experiments 
are common to a number of organisms. The house fly, for example, 
oviposits only in the presence of the odor of fermentation, always has 
a certain form of bacteria on its body in great abundance and the larva 
is unable to survive in garbage which gives an acid reaction. Those 
insects which live in strange media such as strong salt water and petro- 
leum may be associated with microorganisms which have unusual power 
of oxidation. It is likely that the vinegar eel will be found to be simi- 
larly associated with bacteria or fungi. 
In 1915 Loeb^ raised Drosophila on a synthetic medium consisting 
of inorganic salts, sugars and ammonium tartrate. He believed the 
synthetic power of the fly to be as great as that of bacteria. Later^^ 
however, he pointed out that the medium used ''is a well known culture 
medium for certain microorganisms; e.g., yeast cells which are capable 
of synthesizing their proteins and other complicated organic compounds 
from ammonium salts. 
It is very evident from my experiments that the food of Drosophila 
larvae is yeast. The insect depends upon these ceils for its proteins 
and has no greater synthetic power than is common to higher animals. 
Adult flies do not require proteins but survive for a much longer period 
on sugar agar than upon yeast agar. This difference between the nu- 
