DIRECTIONS FOR LABORATORY WORK 763 



(1) Sketch (28) a few isolated cells from a dissociated (macerated) 

 preparation of the liver. Note the number and position of the nuclei, 

 general shape of the cell, character of cytoplasm, cytoplasmic granules 

 (glycogen) and droplets (fat), and cell membrane (?). (Dissociated 

 tissues are best preserved for study in a solution of equal parts of abso- 

 lute alcohol, glycerin and water). 



To a teased fresh preparation of liver in physiologic salt solution add 

 a drop of a 5 per cent, aqueous solution of acetic acid. This will cause 

 the nucleus to appear more distinctly. It dissolves also all albuminous 

 granules, but leaves unaltered fat and lipoids. (This method of treat- 

 ment may be profitably employed with all fresh dissociated (teased) 

 preparations. In the case of the connective tissues, the acetic acid will 

 cause the collagen fibers to swell and finally disintegrate, but will have 

 no effect upon the elastic fibers.) 



Subsequently add to the same preparation a drop of a 1 per cent, 

 solution of methylene blue. This will stain the nucleus and thus cause 

 it to contrast more sharply with the cytoplasm. (Other equally good 

 staining solutions for isolated tissues are: (a) a 1 per cent, solution of 

 methyl green in 20 per cent, alcohol; (b) 1 per cent, aqueous solution 

 of borax carmin; (c) dilute solution of any of the hematoxylin stains; 

 (d) or a 1 per cent, a'queous solution of eosin may be employed to stain 

 the cytoplasm, producing in this way also a heightened contrast between 

 nucleus and cytoplasm.) 



(The best way to add any fluid to a macerated preparation under a 

 cover-glass is to place a few drops of the solution at one edge of the 

 cover-glass, and cause it to flow under the glass by withdrawing fluid 

 from the opposite edge by means of blotting paper.) Distinguish be- 

 tween physical and chemical coloration. 



(2) Sketch (29) a small area of a stained section of the liver. 



(B) SQUAMOUS (Pavement epithelium). 



(1) MESOTIIELIUM. Sketch (30) small area of toto mount of piece 

 of mesentery of cat, treated with silver nitrate solution to outline 

 the intercellular cement and lightly stained with Dtlafield's hematoxy- 

 lin. Note the character of the cell borders, shape of cell, position and 

 shape of nucleus, stomata (?), guard cells (?), and stigmata. Study 

 a stainod section of the amnion. 



(2) ENDOTIIELIUM. Sketch (31) small area of lining of capillary 

 or small vein (e.g., from toto mount of mesentery, or pia mater of 

 brain). Note sinuous <-li;inirlor of cell outline. What is the relation of 



