HISTOLOGICAL DEMONSTRATIONS. 135 



other mode of section, the slices should be immediately placed in 

 rectified spirit. 



e. Staining. The sections may be stained with logwood, silver, and 

 carmine. The last two yield the best results. Carmine may be success- 

 fully used in the following way. Mix equal parts of water, methylated 

 spirit, and Beale's carmine fluid, with all the ammonia retained (see 

 3i8A). (The spirit is added to the mixture in order to prevent the 

 rapid swelling up and solution of the supporting gum.) Transfer the 

 sections from the rectified spirit to the above carmine fluid, and let 

 them remain in this for about twelve hours, until a deep diffuse staining 

 is obtained. Then pour away the carmine and wash the sections very 

 gently with dilute alcohol (rectified spirit I part, distilled water 3 parts). 

 Next cover them with an acid washing fluid, consisting of rectified 

 spirit 60 parts, water 39 parts, hydrochloric acid I part. After wash- 

 ing in this fluid for six or eight hours, until all diffuse staining is 

 removed, cautiously pour off the fluid and preserve the sections in ordi- 

 nary rectified spirit until required. Silver staining is useful for the 

 fresh tissue. It reveals the outlines of the epithelium of the cochlea. 

 The process of staining is the ordinary silver method ( 328). 



f. Mounting. Great care is necessary in mounting the sections, lest 

 important parts be injured. If the sections have not been stained, 

 the gum must be carefully removed or softened by the above, but if 

 glycerine jelly be used for mounting, this precaution is unnecessary. 

 The best preservative media are glycerine, glycerine jelly, and danlmar. 

 The last is only resorted to when the sections have been stained. For 

 unstained, and even for stained sections, glycerine and glycerine jelly 

 are good preservative media. In mounting vertical sections of the 

 cochlea, the modiolus should always be placed across the glass slip to 

 facilitate subsequent microscopical study. 



These methods give good results, and they were to a large extent 

 devised by my late assistant, Dr. Pritchard, to whom I gave this as the 

 subject for a thesis for the University of Edinburgh. 



242. Structure. Examine a series of preparations 

 hardened in chromic acid and unstained or stained with 

 carmine. 



a. (L.) V. S. cochlea showing modiolus. Lamina 

 spiralis ossea and membranacea, with the organ of Corti on 

 the latter. 



b. (H.) V. S. cochlea showing inner and outer rods of 

 Corti, both planted on the basilar membrane. The head 

 of the inner rod resembles somewhat the head of the ulna. 

 The head of the outer rod is articulated with it. A short 

 process passes outward from the head of each rod, to which 

 the membrana reticularis here seen in section is connected. 

 The outer rods are longer than the inner ones. 



