EXPERIMENT STATION BULLETINS. 547 



injection could be observed readily through the body-wall. Since these 

 precipitated sulphides are insoluble in alcohol or oils, histological sec:- 

 tious of tissues treated by this method could be prepared. Figure 3, 

 Plate 1, is a photomicrograph of such a preparation. In this section 

 the cells are not stained, as with a dye, at all. The photograph shows 

 simply the distribution of lead sulphide precipitate through the tissues. 

 Fig. 2, Plate II, is the photomicrograph of another similar prepara- 

 tion. Note that the precipitate is not distributed in all tissues alike. 



Observations made on insects killed in sulphur dioxide gas showed 

 that the proteids of the body were precipitated rapidly by a high per- 

 centage of this gas. In case death was being brought about from the 

 vapor of gasoline, carbon disulphide, chloroform, or other similar 

 volatile substances, however, there was no immediate visible change 

 in the tissues of the insect. No method for obtaining satisfactory color 

 reactions in the tissues, with such fluids, was found. The odor of the 

 vapors might remain on insects some little time after they were re- 

 moved to fresh air; but the best way of proving that they are absorbed 

 was found in the actual volumetic measurement of the amount taken up. 

 The method of doing this can best be given later in this paper. (Page 

 49.) 



WTien insects were dropped into kerosene or gasoline stained with 

 Sudan III, the color did not begin to penetrate the tissues noticeably 

 for several hours. It then slowly made its way. Also it was noticed 

 that the fat body was affected, but not until after several hours. Fig. 

 5, Plate 1, represents a section through the body of a cabbage worm 

 which had lain in kerosene three hours before being fixed in an 

 alcoholic picric acid solution and then prepared for sectioning. Tis 

 sues, in this section, are in just as good condition histologically as those 

 shown in Fig. 4, same plate, although the latter.'is from a section of an 

 insect killed directly by hot alcoholic picric acid. Caterpillars dropped 

 into warm gasoline and left for twelve to fifteen hours, however, had 

 most of the fat removed in solution in the gasoline. Clearly, then, 

 death from these two liquids resulted long before the liquids, as such, 

 had time to penetrate the body. 



Alkaline washes were tried ; full strength Takanap soft soap, full 

 strength creolin, and various dilutions were used. It was found that 

 such washes might be applied to one portion of the body of a cater- 

 pillar, like the cabbage worm for example, until that part was insensible 

 and apparently dead while other parts of the body were alive and yei 

 able to move. Even weak alkaline washes, if kept upon a certain part 

 of the body long enough (fifteen to thirty hours) would be able to 

 penetrate the chitin and kill at the place where the application was 

 made — other portions of the body remaining alive for a time. The 

 proof that this slow penetration took place was found in the effect 

 upon the tissues. Fig. 6, plate 1, is a photomicrograph of a section 

 through a portion of the body of a cabbage worm treated with creolin 

 for thirty hours. The untreated portion of the body of this insect was 

 alive up to the time the tissues were fixed for sectioning. Note that 

 the fat body has gone to pieces and that the muscular tissue has also 

 been attacked. It was instructive to compare such preparations with 

 those that had been treated with kerosene (Fig. 5, Plate 1) or with 

 those on which fixing agents, only, had been used. The two facts then be- 



