448 



THE AMERICAN NATURALIST 



[Vol. LI 



adult flies usually carry living yeast cells upon them this medium 

 would be difficult to use for work in heredity. A nutrient 

 medium for yeast would best suit the needs of geneticists. Into 

 such a food the adults or pupae would carry living yeast cells 

 which would ferment the sugars and produce odorous substances 

 which cause oviposition by the female fly. Larvae on hatching 

 would spread the yeasts throughout the medium, thus increasing 

 growth and alcoholic fermentation which may prevent the de- 

 velopment of injurious microorganisms. 



Two media might be suggested for this purpose, viz. : Fer- 

 mented banana agar and Pasteur's nutrient agar. The former 

 may be prepared by adding two cakes of bread yeast separated 

 in 100 c.c. of water to one dozen mashed bananas, mixing thor- 

 oughly and allowing to ferment for twenty-four hours. This 

 material should be pressed through a sugar sack and the liquid 

 resulting thickened by heating with 1.5 gm. agar-agar per 

 100 c.c. and poured into slant culture tubes, plugged and 

 sterilized. 



A perfect nutrient medium for yeast consists of 10 gm. am- 

 monium tartrate, 10 gm. ashes of yeast, 100 gm. rock candy, 

 1,000 gm. distilled water. This is called Pasteur's culture fluid 

 and can be treated in the same manner as the above but should 

 be sterilized in an Arnold sterilizer for three successive days, as 

 it can not be heated to as high a temperature as the banana with- 

 out preventing jellation. Pasteur's nutrient solution can be ap- 

 proximated by diluting molasses with three parts of water. 



In the two media described above yeasts develop rapidly and 

 furnish abundant food for Drosophila larvae and also produce 

 odors of fermentation which cause the female to oviposit readily. 

 A concentrated food for yeast such as banana flour would prob- 

 ably increase the value of the first medium as this substance is 

 now used for raising yeast in the brewing industry (6). 



REFEREXfES 



1. Baiimberger, J. P., nnd Gln?or. R. W. Seifner. X. S.. XLV, pp. 21-22. 



2. BaumberKcr, J. V. Pr,.. . V,.,'. .1,-. s, .. m, ijo ,0^, 



J. P. Baumberger 



