EXPERIMENT STATION BULLETINS. -539 



in all the tracheae leading from the stigmata. Sudan III is insoluble 

 in water. In a dissection of a large tomato worm made under water, 

 therefore, tracheae containing Sudan Ill-kerosene may be traced 

 beautifully. Fig. 1, Plate 1, is a photograph of such a dissection show- 

 ing several tracheae filled with red oil (black in the photo) near the 

 last two ganglia of the nervous system. It should be noted here that 

 Melmmplus femoratus and the larva of Phlegethontkis celeus are in- 

 sects possessing a closing apparatus in each of the large tracheae lead- 

 ing from the spiracles. Kerosene is able to pass this closing apparatus 

 when applied in sufficient amounts. Kerosene-emulsion and emul- 

 sions of the miscible oils were stained with indigo-carmine or with 

 safranin and then shown to enter the spiracles of insects in the man- 

 ner just described for kerosene. These two stains are carried in solu- 

 tion by the water particles of the emulsion. Indigo-carmine is en- 

 tirely insoluble in absolute alcohol or clearing oils, so that insects 

 treated with a spray or a dip of emulsion containing indigo-carmine 

 may be afterward dropped into absolute alcohol and the stain will be 

 preciijitated just where it happened to be in the insect. Moreover, the 

 tissue may then bo cleared, embedded in paraffin and sectioned for 

 histological study without the least danger of the stain spreading dur- 

 ing the manipulation.' Fig. 2, Plate 1, is a photomicrograph of a sec- 

 tion of a plant-louse prepared according to the method just described 

 after having been treated first with creolin emulsion containing indigo- 

 carmine in solution. The picture shows a plug of the stain precipitated 

 in a trachea at *'a" where it had been carried by the emulsion. 



By such methods it was therefore comparatively easy to demonstrate 

 that these contact insecticides may enter the respiratory system of in- 

 sects in amounts which are often great enough to plug the larger 

 tracheae. f 



DOES PLUGGING OF THE TRACHEAE CAUSE DEATH BY SUFFOCATION? 



Although the insecticide enter the tracheae, it scarcely seemed possi 

 ble that the plugging could be so complete as to cause the compara- 

 tively rapid death which occurs to insects thoroughly treated with 

 gasoline or kerosene. Almost every one has known of beetles or cater- 

 pillars which revived after having lain in water for several hours ap- 

 parently dead. Such instances .indicate that certain insects, at least, 

 are not easily suffocated. 



In an article published in the Journal of Experimental Zoology 

 1906, Eulalia V. Walling relates, among other experiments, instances 

 of the complete recovery of respiration in grasshoppers brought into 

 fresh air after a confinement in pure carbon dioxide for fifteen hours. 

 Other specimens recovered the heart beat in fresh air after having been 

 forty-eight hours in pure carbon dioxide. In hydrogen, this author 

 says that grasshoppers retained the ability to perform respiratory 

 movements, at intervals, over a period of five days continuous confime- 

 ment. 



Truly, these insects were not easily suffocated if they could do with- 

 out oxygen for such long periods. The experiments seemed so very 

 remarkable and so directly applicable to the project that it was de- 

 cided to duplicate them, if possible, in case of the two gases named. 

 For obtaining the gases pure, however, a different method was used — 



