There are three methods that are commonly used to make contact 

 between the specimen and the photographic emulsion. The first is the 

 so-called opposition method, where the specimen is simply placed in 

 contact with the photographic emulsion in the dark. This method is 

 suitable for making autoradiographs of gross specimens or single cells. 

 Paraffin sections of tissue can be floated on warm water and then picked 

 up on a microscope slide which has previously been coated with a thin 

 emulsion film. The sections remain attached to the slide during photo- 



RadioQCtive material 



Photographic emulsion 



Figure 11-36. Schematic Diagram Showing the Principle of Autora- 

 diography. (From Pelc, S. R., 1958. "Autoradiography as a Cytochemical 

 Method, with Special Reference to C^^ and S-^^," in Danielli, J. F. (Ed.), 

 "General Cytochemical Methods," 1, Academic Press, New York, N. Y., 

 Fig. l,p. 280.) 



graphic processing and subsequent staining and mounting. The second 

 is the liquid-emulsion method which involves mounting the specimen on 

 a slide and then coating it with a fluid emulsion that is allowed to harden. 

 Extraction, hydrolysis, or staining of the specimen is generally carried 

 out before application of the emulsion. The third method is the stripping- 

 film technique which has been used extensively in this country and 

 abroad. In this method, a thin-film emulsion is stripped from a glass 

 plate and floated, emulsion side down, on the surface of water. The 

 emulsion film is then picked up with a slide on which the specimen 

 (parafiin sections, squashes) has been mounted. The specimen may be 

 stained before or after it has been covered with the stripping film. 



258 / CHAPTER 11 



