102 THE FROG 



preferred. Paraffin with a melting-point of about 52 C. is 

 best for general use. Thin sections must be cut at a low 

 room temperature, thick sections at a high room tempera- 

 ture. The sections are best cut with a Minot rotary micro- 

 tome. Xylol is usually to be preferred as a clearing reagent, 

 and Canada balsam for the final mounts. Use No. i cover 

 glasses for permanent mounts. 



The following preparations are needed: i. Stratum cor- 

 neum. Shed epidermis (stratum corneum) may be found 

 in the water in which living frogs are kept; this is usually 

 satisfactory for study when preserved promptly in forma- 

 lin. The material should be collected when available, and 

 kept for use when needed. Permanent stained mounts are 

 not necessary but are convenient; to prepare them the ma- 

 terial should be fixed with Zenker's fluid, stained deeply with 

 Delafield's hsematoxylin and slightly destained; a counter- 

 stain is not desirable. 



2. Integument of Amphioxus.- -This furnishes a good 

 example of simple columnar epithelium. From a specimen 

 killed and preserved in formalin, strip off a piece of the in- 

 tegument and treat it with Zenker's fluid to improve the 

 fixation. Imbed in paraffin and cut sections about 8 /* thick ; 

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

 stain with eosin. 



3. Red blood corpuscles.- -For making permanent 

 stained preparations of the red blood corpuscles of the frog 

 the following method is recommended: Fix about 0.5 c.c. 

 of fresh blood in a half -ounce vial containing I per cent, 

 glacial acetic acid saturated with corrosive sublimate. The 

 subsequent processes of washing with weak alcohol, treating 

 with iodized alcohol, staining with Delafield's hsematoxylin, 



