338 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



slide emulsion with 6 ml of distilled water and 1 ml of a wetting agent 

 (Duponol C). 



4. The stained slides are warmed to 37°C, and 2 drops of fluid emulsion 

 applied per square inch. The drops are spread evenly and quickly with 

 a camel's-hair brush, and even distribution is accomplished by tilting the 

 slide. 



5. The slide is maintained at 37°C for 30 to 60 sec on a level surface 

 and then allowed to cool for 30 min on a level surface. 



6. The slides are stored for exposure at refrigerator temperature in a 

 horizontal position in lighttight boxes, which, in turn, are placed in jars 

 containing a drying agent. 



7. The preparation is developed in Kodak D-72 at 18 to 20°C for 

 l}4 min, fixed in acid fixer for 3 to 6 min, washed for 15 min in water 

 below 20°C, and dehydrated in 95 per cent alcohol, absolute alcohol, 

 alcohol-xylol, and three changes of xylol. 



8. The slides are immersed in 1 per cent balsam and mounted in balsam 

 under a cover slip. 



Modifications. Belanger (30) has described an inversion procedure 

 that permits staining of the tissue without any interference from the 

 emulsion. In principle, the unstained celloidin-covered section is coated 

 with fluid emulsion in the usual way. After exposure and photographic 

 processing, the preparation is removed from the slide and sealed to a clean 

 slide, wdth the processed emulsion next to the glass and the tissue surface 

 now available. The tissue can then be stained, and the celloidin protects 

 the emulsion from the staining reagents. 



A 'Svet-process" technique has been proposed by Gomberg (31) which 

 is based on apphcation to the specimen of a celloidin layer containing 

 bromide ions. The specimen is then transferred to a silver nitrate bath, 

 which forms a sensitive layer. The potential of this method arises from 

 the resolution theoretically possible, since the photographic layer is only 

 about 1 ju thick. 



Stripping -film Method. Principle. An emulsion is stripped from its 

 base and flattened over the histological section or smear on a glass slide. 

 The specimen can be stained either before contact wdth the film or through 

 the film base after exposure. Unstained sections can be studied by phase 

 microscopy. 



Advantages. The procedure is somewhat less tedious than the coating 

 method; offers the advantages of even emulsion thickness, good contact, 

 constant registry, and excellent resolution; and permits good correlation 

 of radioactivity with histological structure. Depending upon the method 

 used, the impervious base emulsion may protect the emulsion from the 

 tissue. 



