APPENDIX. 



A PREPARATION OF TISSUES FOR EXAMINATION IN 

 MICROSCOPIC SECTIONS. 



i. Fixation: 



a. It is most important that the tissues to be examined be placed in the fixing 

 fluid as soon after death or operation as possible. Degenerative changes are in this 

 way avoided. 



b. The piece of tissue to be fixed must not be too large. Using a sharp scalpel, 

 or preferably a razor, a slab of tissue about one-half an inch square and not more 

 than one-fifth of an inch thick should be dropped into the bottle containing the fixa- 

 tive. The bottom of this bottle should have a thin layer of cotton with a piece of 

 filter-paper covering it. There should be at least twenty times as great a volume 

 of fixing fluid as of tissue to be fixed. Delicate tissues, as pieces of gut, should be 

 attached to pieces of glass, wood, cardboard, or blotting paper before being placed in 

 the fixative. 



c. The most convenient fixative for the average medical man is a 10% solution 

 of ordinary commercial formalin (4% of formic aldehyde gas), either in water or, 

 preferably, in normal salt solution. Fixation is complete in from twelve to twenty- 

 four hours. By placing in the incubator, at 37 C., two to twelve hours in the forma- 

 lin solution suffices. If fixed in the paraffin oven (56 C.), fixation is accomplished 

 in about one-half hour. 



Formalin once used for fixation must be thrown away. 



The fixative which probably gives the best histological pictures and with which 

 we obtain the most satisfactory haematoxylin staining is Zenker's fluid. This is 

 Miiller's fluid containing 5% of corrosive sublimate. It also contains 5% of glacial 

 acetic acid, which latter is only added just before we are ready to fix the piece of 

 tissue. Miiller's fluid is: 



Pot. bichromate, 2 . 5 grams. 



Sod. sulphate, i . o grams. 



Water, 100.0 c.c. 



Zenker's fluid fixes in about twenty-four hours. After all corrosive sublimate 

 fixatives we should wash the tissues in running water for twelve to twenty-four 

 hours. The precipitate of mercury in the tissues is best gotten rid of by treating the 

 section on the slide with Lugol's solution, rather than the tissue in bulk with iodine 

 alcohol. 



In Orth's fluid we add 10% of formalin to Miiller's fluid (recommended for nerve 

 tissue). 



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