Sept. 3. I9I7 Quassia Extract as a Contact Insecticide 525 



mixing either lead acetate or tannic acid with the solution containing 

 the water extract of quassiin powder (described on p. 520), 4 parts of the 

 quassiin solution were added to i part of aqueous ferric-chlorid solution. 

 Aphids submerged in this mixture for }4 minute, 30 minutes, and 40 

 minutes were then fixed in a fluid made in the proportion of 5 c. c. of 

 absolute alcohol to 5 drops of tannic acid. A black precipitate is thrown 

 down when this acid unites with ferric chlorid. After remaining in the 

 mixture of alcohol and tannic acid an hour, the aphids were removed 

 and were then placed into absolute alcohol to insure better fixation. 

 Since this precipitate, as well as the other precipitates, do not adhere 

 well to insects, no liquid was used for straightening the ribbons on the 

 slides; the sections were pressed against the slides by using the fingers, 

 and as alcohol easily removes such precipitates from sections, most of the 

 sections were not stained, and these were left in the xylol only a suf- 

 ficient time to remove the paraffin. Those sections stained were usually 

 not reliable for tracing precipitates, because some of the precipitate had 

 been lost while the slides were being run through the alcohols, and, 

 furthermore, very often the stain masked the precipitate. 



A study of the foregoing sections showed a small amount of black 

 precipitate on the outside of the integuments of the aphids that had 

 been submerged only one-half minute, but none was seen in the spiracles 

 or in the tracheae; however, in those aphids submerged for 30 and 40 

 minutes much more black precipitate was seen on the outside of their 

 integuments, and occasionally a few small particles in the spiracles and 

 in the tracheae a short distance from the spiracles. 



(b) Tracing Soap Solution Extracts op Quassiia Chips into Aphids 



Aphids on sweet peas and nasturtiums were sprayed so heavily with 

 the soap-solution extract (lA) from quassia chips described on page 515 

 that the solution collected in drops around the legs of the aphids and 

 had not all disappeared 3>< hours later, when the aphids and leaves were 

 fixed. Some of these insects were sprayed with the solution colored 

 with carmine acid; and the others with the solution not containing a 

 stain. The former were fixed in absolute alcohol overnight, and the 

 latter in the fixative described below. Absolute alcohol containing 

 ferric chlorid (FejClg 4- 1 2 HjO) readily precipitates the potassium in 

 the soap solution; but since the water in the ferric chlorid dilutes the 

 absolute alcohol, a good fixation does not result. To avoid this dif- 

 ficulty the ferric chlorid was melted and fused, thereby dehydrating it. 

 Absolute alcohol was then saturated with the resulting cold melt, and 

 after filtering the mixture an amber colored liquid resulted. When this 

 liquid was mixed with the soap solution, a yellowish, flocculent precipi- 

 tate was formed. Those aphids fixed in this fluid were afterwards well 

 washed in pure absolute alcohol to remove the fixative and to insure 

 better fixation. 



