US] COMPARATIVE STUDIES ON NEMATODES— BETH ERINGTON 11 



tendency it has to mask the finer details of structure which one is desirous 

 of seeing when using higher magnifications. This is due to the deep and 

 homogeneous coloration taken on by the cuticula and underlying structures 

 belonging to the bodywall. Best results along the line of toto staining 

 using Carnoy-phenol in the process were obtained by using Orange G, 

 safranin, methyl green, lichtgriin, acid fuchsin, methyl blue, Mayer's HCl 

 carmine and Ehrlich's hematoxylin. 



With the exception of HCl carmine, safranin, and the hematoxylins, 

 all these stains are used by adding the dry powder in very small amounts 

 to Carnoy-phenol and the degree of staining controlled. Safranin is 

 utilized to saturation in 70 per cent alcohol and allowed to strongly over- 

 stain the specimens. Then they are removed to Carnoy-phenol until 

 destaining is sufficient when clearing is at once undertaken. Acid fuchsin 

 is the most tenacious of the stains mentioned and colors very rapidly. The 

 most presentable mounts were obtained by slightly overstaining the speci- 

 mens in the phenol reagent with small quantities of acid fuchsin and 

 lichtgriin added in powder form to make a dark purple solution. Then 

 the cuticula and body-wall musculature are destained by placing the 

 worms in 95 per cent alcohol and passing into it a small quantity of dry 

 ammonium gas. When all color is totally gone and the specimens are 

 white showing no clouds of red coming off, they are returned to pure 

 reagent which again restores the red color, most of which is now only in 

 the internal organs. Clearing and mounting are done as described previ- 

 ously. 



Much greater latitude for observation is better obtained by utilizing 

 degrees of clearing rather than staining. Permanent mounts may be made 

 of glycerine-prepared specimens in glycerine jelly properly sealed against 

 evaporation, or material may be mounted after suitable preparation either 

 in camsal-balsam, cedar immersion oil, or Canada balsam. These four 

 mounting media will give a differential clearing indicated by the following 

 approximate indices of refraction: 1.476, 1.47, 1.520, and 1.535 respectively 

 (Lee 1913). To prepare the specimens for passage into these media, they 

 are first placed in Carnoy-phenol and then brought into the clearing fluids 

 most suitable for passage into the mounting medium. For glycerine jelly 

 mounts, the phenol reagent is replaced by pure glycerine; camsal-balsam 

 is preceded by clearing the material in camsal, a liquid formed by the 

 mutual solution of salol (phenyl-salicylate) and gum camphor; immersion 

 oil follows thin cedar oil; and Canada balsam replaces oil of wintergreen. 

 The process of clearing is accomplished as previously explained. 



Another excellent medium for small, very transparent worms is 

 "Diaphane," a resinous medium employing gum sandarac on the order 

 of Gilson's "Euparal" which, because of its low index of refraction, shows 

 greater detail in the cleared specimens than balsam. The nematodes are 



