414 SPECIAL MICROSCOPIC TECHNIQUE. 



with a weak solution of methylene-blue (1 per cent, in physio- 

 logical salt solution) for from three-quarters to one and one- 

 half hours. This stain is not permanent, but may be made so 

 by treatment with the following fixing fluid of Bethe : am- 

 monium molybdate, 1 gramme ; distilled water, 10 cc. There 

 may also be added hydrogen peroxide 1 cc. and hydrochloric 

 acid 4 drops. 



Tissues remaining in this fluid for from six to twenty hours 

 should be kept on ice. They are then washed in running 

 water and transferred to absolute alcohol for about one-half 



hour. 



13. SKIN. 



61. The stratum spinosum is seen plainly in tissue hardened 

 in osmic acid. The stratum lucidum is yellow in sections 

 stained in picro-carmine. The granules of the stratum granu- 

 losum are stained with carmine or hsemalum. 



62. The mammary gland is studied best after fixation in 

 Flemming's fluid and staining in safranin. The elements of 

 the colostrum can be studied directly on the slide. 



14. EYE. 



63. A negative picture of the spaces and canals of the cornea 

 may be obtained in the following way : The cornea of a fresh 

 eye is deprived of its epithelium and allowed to remain in a 

 1 per cent, silver nitrate solution for from three to six hours in 

 the dark. It is then placed in water in the sunlight, and after 

 reduction has taken place is hardened in alcohol of increasing 

 strengths. Sections parallel to the surface are made and 

 mounted in balsam. The system of canals is colored white 

 on a brown background. 



64. The impregnation of the corneal cells and canals with 

 gold may be accomplished by the gold chloride method (59). 



65. For the study of the finer structure of the retina, the 

 tissue is hardened in Flemming's fluid and thin paraffin sections 

 are stained in safranin. 



66. The nervous elements of the retina may be demonstrated 

 by Ehrlich's methylene-blue method, or by Ramon y Cajal's 



