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RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



4. The film is developed and stained according to one of the procedures 

 outlined in Table 7-2. It is important that heavy staining be avoided 

 on account of uptake by the emulsion. 



Evans and McGinn (28) have recently described a modification that 

 gives three images on the same slide: the tissue alone, the composite 

 tissue-autoradiogram, and the autoradiogram alone. This is accom- 

 plished by use of two adjacent sections, one of which is inverted on the 

 cover slip and is also used to produce an autoradiogram by apposition, 

 whereas the other is mounted permanently on the emulsion. 



^^Emulsion, 



Fig. 7.2. Mounting method. Cut tissue sections are floated on warm water to remove 

 the wrinkles {a), a knife blade heated (6), the sections separated from the ribbon (c), 

 and the sections picked up by placing the plate in the water beneath them (d) to obtain 

 the permanently mounted section shown at (e). [Courtesy of Patrick J. Fitzgerald, Eva 

 Simmel, Jerry Weinstein, and Cynthia Martin, Radioautography: Theory, Technic, and 

 Applications, Lab. Invest., 2: 181-222 (1953), Paul B. Hoeber, Inc., publisher.] 



Coating Method. Principle. The section is covered with a fluid 

 emulsion which is allowed to harden and forms a permanent bond for sub- 

 sequent exposure and processing. 



Advantages. Good contact and constant registry are obtained which 

 lead to good resolution and allow good correlation of radioactivity with 

 histological structure, since the photographic image and section are 

 observed simultaneously. A celloidin layer protects the tissue from 

 photographic processing fluids, and in the inversion method the photo- 

 graphic image is protected from staining fluids. The thickness of the 

 fluid emulsion can be somewhat controlled. 



Disadvantages. The handling of the emulsion tends to increase the 

 background fog, and the preparation of an emulsion of uniform thickness 



