AUTORADIOGRAPHY 335 



plate and section are held together tightly during exposure. Afterward 

 the cover slip can be bent, and the plate then processed without the section 

 coming in contact with the developing and fixing solutions. When the 

 cover slip is released, the section returns to its original position super- 

 imposed upon the autoradiogram. 



Mounting Method. Principle. The sections are mounted on the 

 emulsion and remain permanently bonded thereto throughout the subse- 

 (juent photographic and staining processes. 



Advantages. The methods are relatively simple. The contact, reg- 

 istry, and resolution are good, thus permitting studies on the cellular level. 

 The autoradiogram and section are always in alignment and are observed 

 simultaneously; this allows correlation between structure and photo- 

 graphic image. 



Disadvantages. There are possibilities of radioisotope loss during the 

 fixation and processing of the tissue. There may be spotty development 

 on account of nonuniform penetration of the tissue by the developer. 

 The emulsion gelatin tends to absorb the tissue stain, and also the photo- 

 graphic darkening may be masked by the opacity of the tissue. There is 

 the possibility of chemical effects on the emulsion due to direct contact 

 with the tissue. This technicjue is difficult to use with plastic or celloidin- 

 embedded material. 



Recommended Usage. The mounting method has been widely used for 

 P^^ localization in thyroid tissue. Also, blood smears and bone marrow 

 smears have been studied by applying such samples directly to the surface 

 of the emulsion. 



Typical Method. Details of this method were described by Evans (27), 

 Bourne (8), and Heller (7). The following procedure is essentially that 

 used by Gross et al. (5) and is illustrated in Fig. 7-2 [from Fitzgerald et al. 

 (10)]: 



1. Unstained paraffin sections are floated on water at 40°C to remove 

 wrinkles. They are then transferred to a bath of distilled water at 18 to 

 20°C. Under safelight conditions, the photographic film or plate is 

 dipped into the water under the tissue section, a corner of which is held 

 against the plate, and then removed. After drainage of excess water the 



ection adheres to the emulsion. With blood smears or similar specimens, 

 the sample is spread over the surface of the emulsion, and the preparation 

 rapidly dried in air. 



2. For exposure, the film is stored at refrigerator temperatures in light- 

 tight boxes containing a drying agent. 



3. Prior to development, paraffin is removed by a 1-min treatment in 

 each of two changes of absolute xylol, which is then allowed to evaporate 

 completely since traces may cause photographic darkening; this takes 

 about 15 min. This step is omitted for smears. 



s 



