728 HISTOLOGIC TECHNIC 



Small pieces of tissue, only, should be used. They remain in a con- 

 siderable volume of the solution for three to twenty-four hours, after 

 which they are thoroughly washed in running water for twelve to 

 twenty-four hours, and hardened in graded alcohol. The corrosive 

 sublimate deposits crystals in the tissue. These may be removed by the 

 addition of a crystal of iodin (or tincture of iodin) to the stronger alco- 

 hols until decolorizatiou no longer occurs. If the mercury is not thus 

 removed it will be difficult to obtain well stained specimens, and the 

 presence of the crystals may cause much confusion. In obstinate cases 

 Lugol's solution is recommended in place of tincture of iodin (alcoholic 

 solution of iodin), to be added until the alcohol has a 'port wine' color. 

 (See page 758.) 



This is probably the best fixing fluid for general routine histologic 

 work. The presence of the acetic acid, however, dissolves the more deli- 

 cate albuminous granules. To avoid this, formalin may be substituted 

 in the same proportion, and added in the same way, for the acetic acid. 

 This modified Zenker's fluid (HELLY'S FLUID) is particularly valuable 

 for the preservation of tissues where it is desired to investigate the 

 granular cytoplasmic contents, e.g., blood cells in embryos, etc. 



Flemming's Fluid (strong solution) : 



Chromic acid, 1 per cent, aqueous solution 15 parts 



Osmic acid, 2 per cent, aqueous solution 4 parts 



Glacial acetic acid 1 part 



The mixture should be newly made, from stock solutions of the 

 ingredients, immediately before using. The stock mixture undergoes a 

 deteriorating chemical transformation. 



Pieces of tissue should not be more than 2 to 3 mm. in thickness 

 and should be left in the solution and kept in the dark for one to twenty- 

 four hours, according to the results desired. For mere fixation a short 

 immersion is sufficient ; for blackening fat and the myelin of medullated 

 nerve fibers the longer period is necessary. After fixation the tissues 

 are to be washed in running water for three to twenty-four hours, and 

 hardened in graded alcohol. 



This fluid gives splendid results for the fixation of the finer cyto- 

 logical elements of glandular epithelium; and for the demonstration 

 of nuclear constitution, chromosomes, and mitotic figures, it is unex- 

 celled. It serves also to demonstrate the presence of fat and myelin, 

 which are blackened by the osmium tetroxid. When used for the dem- 

 onstration of fat in sections, chloroform should be substituted for 



