AUTORADIOGRAPHY 325 



The autoradiographic techiii(iue has one appeal to the biologist: elec- 

 tronic equipment is not required. From this point of view the methods 

 may be regarded as relatively simple and inexpensive. However, much 

 the same art and science will be required for meaningful results as are 

 needed for conventional histochemical technique. 



GENERAL CONSIDERATIONS 



Laboratory Requirements. The laboratory facilities should be reason- 

 ably close to the source of the fresh tissue, at least in the same building. 

 It is essential that the facilities not be located in the vicinit}^ of high back- 

 ground levels from radioisotopes or X-ray machines which may produce 

 background fog in the film. Space is required, as determined by the 

 volume and variety of work, for dissection of specimens, routine histolog- 

 ical processing, storage of specimens during and after exposure, photo- 

 graphic processing, examination of autoradiograms, and recording of data. 

 When possible, the space should be divided into individual work areas. 

 The usual laboratory and darkroom service utilities are needed, and it is 

 particularly desirable that room temperatures be controlled. The dark- 

 room should be arranged for convenient operation, with appropriate light 

 locks, constant-temperature water, and adecjuate ventilation, since nox- 

 ious solvents are often employed. In addition to chemical glassware, 

 typical histological equipment is needed such as dissecting instruments, 

 microscope slides, cover glasses, slide boxes, diamond or glass-marking 

 pencils, water baths, staining jars, paraffin oven, microtome, microscope, 

 and refrigerator for storage of films. If large numbers of tissues are to be 

 fixed, it may be w4se to invest in an automatic processing unit. As indi- 

 cated later, equipment such as freeze-drying apparatus and special bone 

 saws may be useful for particular purposes. 



A radiation survey meter is helpful for checking possible contamination 

 and also for measurement of tissue sections in order to estimate exposure 

 times. A line-operated count-rate meter with a thin-mica-end-window 

 Geiger tube has been found satisfactory for this purpose. The amount 

 of radioactivity contained in a thin tissue section will usually be small, so 

 that contamination of the microtome knife or staining equipment is not 

 a serious matter. However, the original tissue samples may contain con- 

 siderable activity, and appropriate health-physics measures should be 

 taken. 



Photographic Emulsions. Extensive discussions of the properties of 

 films, photographic processing, resolving power, and tissue dosage are 

 beyond the scope of this text and have been adequatel}^ covered in general 

 references (4, 11). However, resolution is so important that it is neces- 

 sary to consider this matter, at least qualitatively. If there are two point 



