WAX GLANDS OF THE COCKROACH 567 



exposed. Bouin's fluid proved the most practical for this pur- 

 pose. When the parts were fully extended, they were plunged 

 into hot killing fluid and the pressure maintained until the hot 

 killing fluid without and the killing fluid within had so fixed the 

 material that the parts would remain extended when the pressure 

 from the hypodermic needle was released. 



For histological study the material was fixed in Fleming's 

 (strong fluid), Gilson's, Zenker's, Bouin's, and Dietrich's fluids. 

 Best cytological results were obtained with Fleming's, although 

 Dietrich's and Bouin's fluids gave almost as good results. With 

 both of the latter more rapid penetration certainly was obtained. 

 Gilson's and Zenker's fluids gave almost similar results. 



At first, material was imbedded entirely in paraffin, but when 

 sections were cut, it was found that the chitin was very brittle 

 and broke very readily, often catching on the edge of the knife 

 and tearing gaps through the entire section. Because of this, 

 sections w^ere so mutilated that they were often useless, espe- 

 cially as the parts desired for study were immediately under the 

 chitin. To obviate this diflficulty several methods were tried 

 either to soften the chitin or else to hold the parts in place so 

 that they would maintain their normal position as nearly as pos- 

 sible. Metalinkoff's method, by which the object was first im- 

 bedded in paraffin in the usual way, and then all the paraffin 

 scraped from the surface of the chitin, the object immersed in 

 Eau de Javelle for twenty-four hours, and re-unbedded, did not 

 give good results. But as this method was tried in only a few 

 cases perhaps repeated trials would have proved more successful. 

 Bedau's 'Seifenspiritus' method gave no results, although fol- 

 lowed as exactly as possible. 



The combined paraffin and celloidin method was also used. 

 Three different modifications of this method were employed — 

 Gilson's rapid process. Apathy's method, and Hoffman's method. 

 All three gave good results, and longitudinal sections through 

 the entire abdomen, 5 micra thick, were easily obtained. 



Cross and longitudinal sections of the entire abdomen were 

 cut from 4 to 10 micra in thickness. These were fixed to shdes 

 by means of the Mayer albumen-and-water method. Instead, 



