4. Transfer to a 4 per cent ferric alum solution for 2 hours.
5. Wash in water.
6. Stain in 0.5 per cent watery hæmatoxylin solution for 30 minutes. Differentiate in the ferric alum solution until the nuclei are dark and protoplasm colorless; control under the microscope.
7. Wash in water 3-6 hours.
8. Counterstain in 1 per cent solution of Ehrlich’s neutral red until section is yellow-red.
Nuclei blue-black; cell-inclusions yellow- to copper-red.
V. CHOLESTERIN. Cholesterin is soluble in absolute alcohol, xylol, ether and glacial acetic. It occurs in the tissues in characteristic rhombic plates often showing a square notch in one corner. In sections from which the cholesterin has been dissolved its presence may be told by the appearance of “cholesterin-clefts” in the tissue, or often in the protoplasm of large foreign-body giant-cells (“cholesterin-giant-cells”). With concentrated sulphuric acid, sections or material containing cholesterin become yellow and then rose-pink. Lugol’s gives it a brown color which turns blue-violet after the addition of sulphuric acid, and exhibits a play of colors, blue, green, to red.
VI. CLOUDY SWELLING. This is best seen in the fresh state in cells obtained by scraping or teasing, or by the examination of frozen sections. Osmic acid, sudan III, scarlet R. ether, alcohol and acetic acid may be used to differentiate from fatty degeneration. The ordinary fixing and staining methods give good pictures, except for slight degrees of the change. These are sometimes wholly lost as the result of the contraction due to the fixation.
VII. COLLOID. (See Epithelial Hyalin.)
VIII. CORNIFICATION. Horn takes the plasma stains (eosin, picric acid, etc.). Van Gieson’s makes a good differential stain. With Gram’s method horn stains deep blue, and with the Ehrlich-Biondi-Heidenhain method it stains red. After fixation in Flemming’s it may be stained with safranin or gentian-violet. Keratohyalin occurs as fine granules in the cells of the stratum granulosum. They stain by hæmatoxylin, carmine and Gram’s method, or may be demonstrated by means of special stains. Eleidin stains with carmine and the fat-stains, but not with hæmatoxylin.