RADIOAUTOGRAPHY 157 



radioactive sulfur in the wheat kernel, employed paraffin sections 

 25-50 p. thick which were covered directly by a layer of aluminum 

 foil 0.8 jx thick. The sensitive photographic surface was placed in 

 contact with the foil. 



The greater the distance between the tissue and the photosensitive 

 surface, the poorer the resolution in the radioautograph due to 

 scattering of the radiation. It is preferable that this distance be kept 

 under 1 mm. Ultraspeed x-ray film has been extensively used, but 

 it has the disadvantage of producing grainy enlargements. Harrison, 

 Thomas, and Hill (1944) recommend a fine grained panatomic film 

 when it is possible to have longer exposures. The photographic film 

 over the sections on a glass slide is covered with another slide and 

 the whole bound firmly together with cellulose tape. All of these 

 operations are carried out in a dark room, of course. After wrapping 

 the slide in light-tight black paper, it may be placed in a cold place 

 for the duration of the exposure. It is advisable to keep the sections 

 cold to inhibit any tendency toward diffusion of the radioactive 

 element. After exposure, the sections are stained in the usual manner 

 to bring out their morphology, and compared to the developed 

 "autographs" with the aid of a dissecting microscope. 



More recently, Belanger and Leblond (1946) extended the useful- 

 ness of radioautography by the ingenious expedient of spreading a 

 photographic emulsion directly on the sections. This not only permits 

 a more intimate contact between the tissue and the photographic 

 surface, but it obviates the matching of the "autograph" to the cor- 

 responding histological detail, which is particularly difficult at higher 

 magnifications. The possibilities of this technique merit a more 

 detailed description of the procedure. 



Belanger and Leblond Technique 



Preparation of Photographic Emulsion. Soak lantern slide 

 plates (medium contrast, Eastman) in distilled water at room 

 temperature. When the gelatin swells, remove from the water. With 

 a glass knife scrape off the gelatin, and melt it in a beaker placed 

 in a 35-40° bath. Carry out this procedure and all others in which 

 the emulsion is used in a dark room. A Wratten "Safelight — No. 1" 

 (Eastman) may be used at a distance of about 3 ft. 



