APPENDIX 



A PREPARATION OF TISSUES FOR EXAMINATION IN 

 MICROSCOPIC SECTIONS 



Note. The most important step in the preparation of sections of tissues for histological 

 examination is proper and immediate fixation. This step in the technic is often 

 in the hands of the surgeon at the time of the operation or the physician at autopsy 

 and it should be understood that a satisfactory diagnosis can only be made when 

 the pieces of tissue are at once dropped into a fixative. Various protozoa, as amoebae, 

 disintegrate in one or two hours, unless properly fixed and body cells show degen- 

 eration after the tissues have been left without fixation for a few hours, which 

 changes may be interpreted as pathological. 



Prepare a pint or quart of 10% formalin solution (4% formaldehyde) shortly 

 before operation or autopsy. Drop into the solution slices of tissue, not more than 

 *y inch thick, as soon as cut. Leave in the fixative for twenty-four hours and 

 then place in 70% alcohol. The pathologist will attend to the other steps. 



We use two fixation solutions in routine work, one of 10% formalin and one of 

 Zenker's solution. This latter requires prolonged washing of tissues following 

 fixation and has little advantage over formalin for ordinary purposes. 



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 20 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 (i) 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 37C., two to twelve hours in the forma- 

 lin solution suffices. If fixed in the paraffin oven (s6C.), fixation is accomplished 

 in about one-half hour. 



Formalin once used for fixation must be thrown away. 



(2) 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 



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