PAVEMENT EPITHELIUM. 4:6 



Kill a large frog by decapitation, and open the abdomen freely by 

 an incision along the median line. Pull out the intestines by grasping 

 the stomach with the forceps. This will expose the small intestine, 

 which you will remove, together with the attached mesentery, by 

 means of quick snips of the scissors. Work as rapidly as possible and 

 avoid soiling the tissue with blood. Throw the gut into a salt-cellar 

 filled with silver solution, vide formulae, where it must remain for ten 



FIG. 27. PAVEMENT EPITHELIUM FROM FROG'S MESENTERY. SILVER STAINING. 



A. Area showing the- outlining of the pavement cells by the silver-stained cement sub- 

 stance. The nuclei have been brought out by the carmine. Minute stomata may be seen be- 

 tween certain cells. 



B. A blood capillary terminating below in an arteriole. The silver has outlined the en- 

 dothelia of the vessels. 



C. An area showing both layers of the pavement. The deeper cells are faintly outlined, 

 being out of focus. The silver has been deposited over the lower portion of the specimen, 

 nearly obscuring the cement lines. X 250. 



minutes covered from the light. Lift the tissue from the solution by 

 means of a strip of glass (or a platinum wire), and throw into a saucer 

 of clean (preferably distilled) water, changing the latter repeatedly for 

 ten minutes. After washing, and while yet in the water, expose to 

 sunlight (perhaps fifteen minutes) until a brown tint is acquired which 

 indicates the proper staining. 



