THE FROG IO3 



destaining with acid alcohol, etc., should be carried on in 

 this vial, time being allowed for the corpuscles to settle each 

 time before the liquid is decanted or removed with a pipette. 

 From 70 per cent, alcohol mount a drop of the liquid con- 

 taining the corpuscles on a slide previously smeared with 

 albumen fixative, and allow the corpuscles to settle and ad- 

 here to the slide. Before the alcohol has entirely evaporated 

 from the slide, counterstain with eosin, dehydrate in the 

 higher alcohols, clear in xylol and mount in balsam. This 

 method saves time in case a large number of slides are to be 

 prepared; it preserves the form of the corpuscles, makes a 

 clean preparation and allows some of the corpuscles to pre- 

 sent an edge view. 



4. Cartilage taken from entire frogs hardened in forma- 

 lin in the usual way is seldom in good condition, since the 

 formalin does not penetrate quickly enough. Material for 

 histological study should be prepared by placing the fresh 

 femur, sternum or other parts of the skeleton containing 

 hyaline cartilage, in 10 per cent, formalin; or the fresh car- 

 tilage may be examined in normal salt solution. Freehand 

 sections should be cut with a razor. Permanent stained 

 mounts are more convenient to use but are otherwise less 

 satisfactory; to prepare them, fix the material in Zenker's 

 solution, imbed in paraffin and cut thin sections with the 

 microtome; stain on the slide with Delafield's haematoxylin 

 and counterstain with picric acid. 



5. Reproductive cells.- -The ovary of a young frog or 

 salamander should be fixed in Zenker's fluid, imbedded in 

 paraffin and cut into transverse sections about iop thick. 

 Stain on the slide with Delafield's hsematoxylin and counter- 

 stain with Congo red. 



