14 MANUAL OF HISTOLOGY. 



place. Examine at first with a low power, and then with a 

 higher one, until the specimen has been studied in all its 

 details. 



THE ORDINARY METHODS OF PREPARING TISSUES. 



Mullef s fluid. It is customary to use Muller's fluid to 

 render tissues firm, so that they may be easily cut with the 

 knife, and made thin enough for microscopic studies. The for- 

 mula is (by weight) bichromate of potassium, 2 parts, sulphate 

 of soda, 1 part, distilled water, 100 parts. This fluid, which 

 is of a brown color and transparent, is admirably adapted for 

 hardening and preserving permanently nearly all the tissues of 

 the body ; though for the brain and cord it is unsatisfactory 

 without the subsequent use of other reagents. It is, however, 

 very cheap, and specimens may be preserved in it for years, 

 and still retain the characteristics which make them suitable 

 for microscopic study. 



Potassium bichromate solution. Some microscopists prefer 

 simply a solution of the bichromate of potassium (gr. xv. 5 ]) 

 It is well, in this case, to put the specimens into a fresh solution 

 every day for several days. Subsequently they are to be hard- 

 ened in alcohol. The strength of the latter should at first be 

 eighty per cent., then ninety per cent., and finally may be 

 ninety-five per cent. The alcoholic process requires a few ad- 

 ditional days. Solutions containing chromic acid or the bi- 

 chromates are objectionable if the specimen is to be used for 

 coarse demonstration, because the yellow or brown color of the 

 acids is difficult to remove. Prolonged soaking in distilled 

 water will accomplish a great deal, but the final color is gener- 

 ally a clay brown. Of course this objection does not apply to 

 microscopic sections, and indeed it appears as if the chromic 

 acid and chromate solutions prepare them particularly well for 

 the process of staining in various colors. 



Ammonia bichromate solution. Gerlach has recommended 

 this reagent in one or two per cent, solutions for hardening the 

 brain and cord. It is to be used as the preceding (Frey). 



Alcohol and acetic acid mixture (Lockhart Clarke). Two 

 objects were sought by their combination : one to coagulate 

 albuminous matters by the alcohol, the other to render them 

 transparent. The proportion was alcohol three parts and 



