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 or cardboard. 



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 12 to 24 hours. 

 By placing in the incubator, at 37 C., 2 to 12 hours in the formalin 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 

 Muller'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. 

 Muller's fluid is: 



Pot. bichromate, 2.5 grams. 

 Sod. sulphate, i.o grams. 



Water, t 100.0 c.c. 



Zenker's fluid fixes in about 24 hours. After all corrosive sublimate fixatives 

 we should wash the tissues in running water for 12 to 24 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 Muller's fluid (recommended for 

 nerve tissue). 



A saturated corrosive sublimate solution in salt solution with the addition of 5% 

 of glacial acetic acid may be used as a substitute for Zenker's fluid. 



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