162 PKACTICAL HISTOLOGY [XX 



NOTES. 



Hardening. The best hardening agent for salivary glands is per- 

 haps alcohol ; 75 p. c. for a day, then 95 p.c. for a week to a fortnight 

 (absolute alcohol may be used for the second week). The alveoli 

 can be obtained a little separated from one another by injecting the 

 gland artery first with salt solution, and then with 75 p.c. spirit. 

 When absolute alcohol is used to harden a gland the outside is usually 

 much shrunken, this part should be cut away. Sections of glands 

 hardened in alcohol or in mercuric chloride often become sticky 

 when placed in water, this can be prevented by placing the gland in 

 chromic acid -2 p.c. for 1 to 2 days. 



But any of the usual hardening agents may be used thus, 

 mercuric chloride, chromic acid and alcohol, formol and alcohol, 

 Flemming's fluid. 



Staining. The demilunes of the mucous gland are generally best 

 seen in sections of gland hardened in osmic acid 1 p.c. or an osmic 

 acid mixture, stained rather deeply with haematoxylin, and left in 1 p.c. 

 acetic acid for a day. This method also shows distinctly the (artificial) 

 network of the mucous cells. The demilunes may also be stained 

 with acid magenta. 



Mucin may be stained with methylene blue, toluidin blue, thionin, 

 saffranin, or bismarck brown (cp. p. 326), but where there is much 

 mucin, it is generally best to leave it unstained. Haematoxylin does 

 not stain mucin in sections hardened in alcohol, when used in the 

 manner given in the text (p. 35), but does stain deeply mucin 

 granules fixed by osmic acid vapour ; the statement that it stains 

 mucin and not mucigen rests on no satisfactory basis. 



The granules of the serous glands are in some cases preserved by 

 hardening in a mixture of equal parts of 5 p.c. potassium bichromate 

 and 2 p.c. osmic acid. (Altmann's method.) 



Osmic acid vapour for preserving mucous granules. A small bottle 

 is half filled with 2 p.c. osmic acid, corked and left for a day. A 

 hedgehog quill is stuck in another cork. Small pieces 2 to 4 mm. in 

 diameter of a fresh gland, which have not come in contact with 

 blood or any fluid, are placed on the quill, to which they will adhere. 



