June, '16] PARKER: DISPERSION OF MUSCA DOMESTICA LINNAEUS 33? 



in 20 c.c. of 95 per cent alcohol and added to 180 c.c. of water; aqueous 

 eosin, 4 c.c, water, 100 c.c; trypanblau, 4 c.c, water, 100 c.c; methy- 

 lene green, 4 c.c, water, 100 c.c. 



In preparing the rosolic acid solution it was found necessary to dis- 

 solve the crystals in 95 per cent alcohol and then add this solution to 

 the water. The trypanblau used was old and but very slightly soluble 

 in alcohol. 



Use of Stains. — The stains were applied to the flies while in the 

 traps by means of separate small glass atomizers, except that the 

 Sales Yards flies captured in a larger trap were stained with spray from 

 a large tin atomizer. The stain in all cases was applied at the point of 

 release so that stained flies were never transported from one point 

 to another. 



Methods of Killing and Differentiating Flies 



As soon as traps were brought into the laboratory each was placed 

 in a five-pound lard pail and the flies killed by ether, which was found 

 to be more satisfactory than chloroform. 



For examination the flies were spread in a thin layer on a newspaper 

 and were first sprayed with 50 per cent alcohol. Fuchsin, eosin and 

 methylene green entered into solution and left a spot under each fly 

 marked with these stains. The number of stained specimens was im- 

 mediately recorded and the flies again sprayed with a weak alkaline 

 solution (Na O H). Flies stained with rosolic acid became a bright 

 scarlet and left a corresponding spot on the paper while trypanblau 

 left a blue spot. 



It sometimes happened that there was uncertainty regarding the 

 color left on the paper, except, of course, when the mark was blue or 

 green. The other stains were then differentiated by the following 

 tests. The fly responsible for the spot in question was placed in a 

 very small homeopathic vial and about | c.c. of 50 per cent alcohol 

 added. If the stain was eosin the yellowish tint imparted to the solute 

 was a distinct proof. Sometimes the amount of stain was so small 

 that the tint was scarcely perceptible. In this case a small amount of 

 the alkaline solution was added; if fuchsin was present the color dis- 

 appeared, if eosin it remained constant, and if rosolic acid it be- 

 came greatly intensified. If these tests were not decisive no record 

 was kept. The process was repeated with the flies from each station.* 



* At the end of the season a trap was examined which had been in place for- a month 

 at the Sales Yards. It was found that flies marked with rosolic acid yielded a yellow- 

 ish brown color when sprayed with the alcohol solution. Possibly the acid underwent 

 some chemical change during its long exposure to the air, but the scarlet color after- 

 wards appeared when sprayed with the Na O H, but much fainter than normal. 

 The records from this trap are not given. 



