FIXATION 643 



still better results when combined with a nuclear fixative such as 

 acetic acid. The following is an excellent method for general use : 



Mercuric chlorid 7 grm. 



Sodium chlorid 0.75 grm. 



Distilled water 95 cc. 



Just prior to use add 5 cc. of acetic acid. 



Small pieces of tissue remain in this fluid for two to twenty- 

 four hours, and are then transferred to graded alcohol (page 642), 

 remaining twenty-four hours in each strength. Most dyes will act 

 perfectly on tissue fixed in this way. If, however, the presence of 

 mercury interferes with the action of a dye, this salt can be readily 

 removed by the addition of a few crystals of iodin to the graded alco- 

 hol, renewing the iodin if necessary until it is no longer decolorized. 



Formalin. Tissues may be fixed in formalin or formol, a 40 

 per cent, solution of formaldehyde gas, which is to be used in 

 strengths varying from 5 to 20 per cent. Small pieces should be 

 left in the weaker solutions (5 to 10 per cent.) from six hours to two 

 days, not longer. In the stronger solutions (10 to 20 per cent.) 

 tissues should remain for only two to six hours. More prolonged 

 immersion in the fixative causes considerable swelling. As a rule, 

 the stronger solutions are preferable : this is especially true for the 

 fixation of the cells of lymphoid tissue. 



After fixation, the tissues are washed in running water for 

 three to twelve hours and then hardened in graded alcohol. This 

 method gives excellent results with lymphoid and epithelial tissues, 

 but does not bring out the finer details of cytoplasmic structure. 



Potassium Bichromate. This salt has been used in all sorts of 

 combinations ; those which follow are to be specially recommended. 

 Miiller's solution is employed for the fixation of the tissues of the 

 central nervous system, and must be used when fixation is to be 

 followed by any of the Weigert hematoxylin staining methods. 

 Applied to the fixation of other organs, Miiller's fluid is apt to 

 produce some maceration and better results are usually obtained 

 with Miiller-formol or with Tellyesniczky's solution. 



For the special fixation of cytoplasmic granules, and also for 

 after staining with Mallory's connective tissue stains, Zenker's 

 solution yields the best results. 



Miiller's Solution : 



Potassium bichromate 2.5 grm. 



Sodium sulfate 1 grm. 



Water.. . 100 cc. 



