288 HISTOLOGICAL TECHNIQUE. 



(j. Flemming's Solution. — Tins is a solution containing osniic acid, 

 chromic acid, and acetic acid. It does not keep well, and it is best 

 to prepare it just before it is to be used. For this purpose the 

 following stock solutions may be kept on hand : 



A. 2 per cent, solution of osmic acid in 1 per cent, chromic acid. 



B. 1 per cent, solution of chromic acid in distilled water. 

 Osmic acid mav be bought in sealed tubes containing either i or 1 



gram. To prepare the stock solution " A," the tube should be washed 

 on the outside and a deep file-scratch made near its centre. It should 

 then be broken into a bottle containing 50 cc. of a 1 per cent, solution 

 of chromic aid in distilled water. The halves of the tube should be 

 dropped into the bottle and its contents shaken at intervals until 

 solution is effected. This solution had best be kept in the dark 

 to avoid decomposition of the osmic acid. When required for use, 

 prepare the Flemming's solution by mixing : 



Solution " A," 4 cc. 



Solution " B," 15 " 



Glacial acetic acid, 1 " 



Flemming's solution is especially useful for fixing the finer details 

 of structure within the cell. It was devised for the preservation 

 of the mitotic figures formed during karyokinesis, but its range of 

 usefulness far exceeds that limited application. Its power of pene- 

 tration is very slight and the pieces of tissue selected for fixation 

 must be small. They should not exceed 2 mm. in their least 

 measurement, and thinner pieces are apt to give better results. 

 Owing to the presence of osmic acid, Flemming's solution stains 

 fat a dark-brown or black color, and may be used as a reagent for 

 the identification of fatty substances. 



Tissues should be left in Flemming's solution for about twenty- 

 four hours, though twice that length of time would cause little if 

 any harm. They must then be thoroughly washed in running water 

 for twenty-four hours or longer, and hardened in alcohol. Since 

 Flemming's solution is usually employed for the study of the 

 individual cells, it is desirable to prepare very thin sections of the 

 tissues that have been hardened in it. For this purpose embedding 

 in paraffin is the best method. 



The foregoing fixing solutions will meet most of the requirements 

 of the practitioner of medicine, but it frequently happens that he 



