440 Phylum Arthropoda 



Pearl (1926) has recommended a synthetic medium, made up as fol- 

 lows: 



Solution A Solution B 



Cane sugar 500 gm. Agar 135 gm. 



K Na C4H4O6 4H2O 50 gm. Tartaric Acid 30 gm. 



(NH 4 ) S0 4 12 gm. KH 2 P0 4 6 gm. 



Mg SO4 7H2O 3 gm. Water to make 3000 cc. 



Ca Cl 2 15 gm. 



Water to make 3000 cc. 



Dissolve the agar in solution B by heating; mix equal parts of solutions 

 A and B ; use 50 cc. per culture bottle. 



The advantage claimed for this medium is that it is constant. Other 

 workers have failed to find it satisfactory, and real constancy may 

 hardly be attained without accurate control of the yeast supply. 



Several workers have used different materials, when bananas or corn- 

 meal were difficult to obtain, as in certain foreign countries. Bridges 

 and Darby (1933) describe several of these media; Komai (1927) and 

 Gershenson (1928) are original references for two of them. None of 

 these media have proven as generally satisfactory as the three described 

 above. 



As shown by Baumberger (1919), dead yeast may be substituted 

 for live as food for Drosophila larvae. This is the basis for the usual 

 technique for keeping bacteriologically sterile cultures, though these 

 may also be maintained by seeding with bacteria-free yeast cultures. 

 For the methods used in these studies, see the papers of Delcourt and 

 Guyenot (1911), Guyenot (191 7), Baumberger (19 19) and Northrop 



(1917). 



EQUIPMENT AND PROCEDURE 



Half-pint milk bottles are very satisfactory for breeding-jars. Pints 

 or quarter pints may be used, but for most purposes are less convenient. 

 Bridges (1932) has developed a special bottle (that may be purchased 

 from the Illinois Pacific Coast Company, Los Angeles, California) which 

 has side walls that converge from the bottom, thus helping to prevent 

 the block of agar medium from shaking loose. My own opinion is that 

 this is a minor advantage; but workers who depend less on the photo- 

 tropism of the flies for emptying the bottles do not agree with me (see 

 below, under etherizing bottles). 



Paper toweling is usually placed on the medium, in folded squares 

 about 3 inches broad. This serves to absorb surplus moisture and de- 

 crease the danger of drowning the adults. Filter paper or toilet paper 

 may be substituted; even newspaper has been used. Many workers 



