IOO 
Journal of Agricultural Research 
Vol. VII, No. 3 
whether water and nicotine solutions, applied under the most favorable 
conditions, are able to enter the spiracles, mouths, and anal openings of 
various insects. In order to follow these liquids, they were colored with 
various stains. 
(a) ABILITY OP COLORED LIQUIDS TO ENTER THE SPIRACLES AND ALIMENTARY CANAL 
A small quantity each of water and of pure nicotine solution (i: ioo) 
was colored with each of the following aqueous stains: Carmine acid 
(Griibler's Carminsaur), eosin, gentian violet, Delafield’s, Ehrlich's, and 
pure hematoxylins, methylene blue and safranin. Cabbage aphids 
were submerged in each of these colored liquids for an hour. After 
removal from the liquids they were well washed in water, then crushed, 
and finally mounted on slides in glycerin. The glycerin did not mix with 
nor scatter the stains. Various parts of the integuments were colored 
more or less with each stain, but methylene blue seemed to penetrate 
the integuments the most readily of any of these stains. Each stain 
seemed to pass into the tracheae more or less, but the four following ones 
entered most readily: Carmine acid, gentian violet, methylene blue, and 
safranin. Of these four, carmine acid proved to be the best. The 
tracheae in most of the aphids showed scarcely any of the stain, while 
those in the remaining ones showed it conspicuously. In these few 
insects all the larger tracheae in the abdomen, thorax, and head were 
stained; and occasionally a stained trachea was traced into a leg. There 
seemed to be no difference in permeability between the stains dissolved 
in water and those dissolved in the nicotine solution. 
The preceding experiments were repeated by submerging roaches 
{Periplaneta americana L.), croton bugs (. Blattella germanica E.), house 
flies, and larvae of blow flies ( Calliphora vomitoria L.) for an hour in 
water and in a pure nicotine solution (i: 500), each being colored with 
carmine acid. The stain was observed in the esophagus and anus of the 
roaches and croton bugs; in a few of the larger tracheae and in many 
of the smaller ones and in the hind gut of the fly larvae. The house flies 
were fixed in absolute alcohol, which readily throws down carmine acid. 1 
One of the flies that had been submerged in the colored nicotine solution 
was sectioned, and the sections were placed in xylol alone without being 
stained, in order that none of the “precipitated” carmine acid might be 
lost. A study of the sections showed the “precipitated” carmine in 
several of the larger tracheae (PI. 1, fig. A, pr). An examination of the 
other flies showed that the colored liquid had passed into some of the 
larger tracheae and into the rectums. 
The preceding experiments were repeated by submerging green peach- 
aphids ( Myzus persicae) in pure nicotine solution (1:500), colored with 
1 Absolute alcohol does not precipitate carmine acid nor indigo-carmine, but merely throws them out 
of solution, because they are not soluble in it. For lack of an appropriate term to describe these stains 
when thrown out of solution the word precipitate in quotation marks may be used. 
