SOME HARDENING AGENTS. 377 



The only objections I know of to this agent are : — Micro- 

 organisms in tissues do not stain after it ; tissues must be cut into 

 small pieces, not more than quarter to half inch cubes, which is not 

 good when the form of a growth or a 7nacroscopical specimen is 

 required. Staining must also be done, in most cases, with logwood 

 or aniline dyes, for carmine will not stain well. Tissues get brittle 

 if over-hardened, as they do in all re-agents ; otherwise, it is the 

 most excellent agent we have for all tissues, including even the 

 nervous system, when the tissues may be cut in small pieces. 



Flemming's Solution is excellent for embryonic specimens, 

 dental histology, embryology, and mitosis. Its composition is — 

 Chromic Acid (i per cent, solution) ... 40 cc. 



Osmic Acid (2 per cent, solution) ... 12 cc. 



Glacial Acetic Acid ... ... ... 3 cc. 



Pieces of tissue must be very thin, not more than two to three 

 millimetres in size. They will harden in from ten to twelve hours, 

 and after being hardened must be washed in running luater for 

 hours, and then finished in alcohol of various grades from weak to 

 strong. 



Fol's Solution is well known and is very similar, but has less 

 osmic acid, and is used more generally on account of less expense. 

 Osmic Acid (i per cent, solution) ... 2 cc. 



Chromic Acid (i per cent, solution) ... 25 cc. 



Glacial Acetic Acid (2 per cent, solution) ... 5 cc. 

 Distilled Water ... ... ... 68 cc. 



For both Flemming's and Fol's solutions materials must be cut 

 and stained immediately, as after keeping they do not stain well. 

 Saffranin and logwood are the best staining agents for these 

 methods. 



Rabl's Fluid is made by taking 



Chromic acid (i/3rd per cent, solution)... 200 cc. 

 Formic Acid ... ... ... 4 or 5 drops. 



It must always be freshly prepared, the tissues must be fresh, 

 and cut in small pieces. Harden for from twelve to twenty-four 

 hours ; then wash thoroughly in distilled water, and finish in 

 various grades of alcohol. Stain with hsematoxylin or saffranin. 

 It is especially valuable for mitosis and nuclei generally. Its 

 advantage is that tissues hardened in it do not afterwards darken. 



