198 Journal of Agricultural Research voi. xvii.no. s 



small pieces and were fixed in a liquid containing equal parts of absolute 

 alcohol and chloroform with corrosive sublimate to excess. The thick 

 celloidin completely covered the integuments of the dusted insects and 

 held the particles of powder where they were already adhering to the 

 hairs and integuments. It did not pass into the mouth, anus, or spiracles 

 but ran into all of the crevices and surrounded the hairs. The 

 chloroform soon made the celloidin hard, thereby forming a hard layer 

 around the insect, and thus holding the powder in position. Sections 

 made from this material were stained with eosin in equal parts of absolute 

 alcohol and chloroform. This method kept the celloidin hard and thus 

 firmly held the particles of powder in position. 



A study of the sections described above showed the following : A thick 

 layer of celloidin, dotted with particles of powder, completely surrounded 

 the integument, and processes from it ran into all of the crevices or inden- 

 tations of the integument. The heat in the paraffin bath caused the 

 celloidin to shrink, thereby drawing it away from the integument at 

 places ; but at other places it remained in contact with the integument. 

 Most of the powder in the layer of celloidin lay against the integument 

 and none could be seen inside the insect, except particles here and there 

 which seemed to have been dragged inside by the microtome knife; none 

 was seen in the tracheae and only occasionally was a small amount 

 observed in the spiracles, but never enough to clog them. 



To be able to trace the powder better and distinguish it irom the par- 

 ticles of food in the intestine, the following experiments were performed: 

 Eight fall webworms were dusted with a mixture of Derris powder and 

 lamp-black, and eight more with a mixture of Derris powder and carmine; 

 the lamp-black and carmine were finely pulverized and were mixed thor- 

 oughly and in equal proportions with the Derris powder. The first four 

 of each set were three hours later fixed intact in the modified Carnoy's 

 fluid (equal parts of absolute alcohol, chloroform, glacial acetic acid, and 

 corrosive sublimate to excess) ; and the second four of each set were 

 treated by the celloidin process, described above. Many sections were 

 made from the material of each set; one-half of those from the material 

 dusted with the Derris powder and lamp-black mixture were stained in 

 the mixture of absolute alcohol, chloroform, and eosin; and the other 

 half were left in the paraffin-ribbon stage on the slides and not stained. 

 The sections from the material dusted with the Derris powder and carmine 

 mixture were likewise treated, one-half being stained with methylin blue 

 in 95 per cent alcohol and the other half being left unstained in the par- 

 afRn-ribbon stage. 



A study of these sections showed the following: The black and red 

 powders were easily traced around the outside of the integuments but 

 never in the tracheae, and only occasionally did a small amount lie in 

 the mouth of a spiracle. In many of the sections, small masses of the 



