Processes of Identification in Histochemistry 9 



sion of energy-rich radiation by suitable isotopes. The tissue 

 sections are mounted directly on a photographic emulsion, 

 which, after a certain length of exposure, is developed. The 

 unreacted silver halide is removed by hypo ( Na thiosulf ate ) , 

 and the section can be stained by one of the conventional 

 histological staining methods. Radioactive substances are 

 revealed by local blackening of the emulsion. 



4. Physicochemical.— In this class belong methods which 

 attempt to obtain information about the dissociation con- 

 stants of protein substances by staining them with dyes 

 buffered at various pH levels. As will be shown, the validity 

 of inferences drawn from the results of this method is open 

 to doubt. 



5. Microincineration.^— This technique cannot be fitted 

 easily into any of the previously mentioned classes. Consider- 

 able experience is required for the evaluation of spodograms; 

 however, it seems that at least Fe and Si can be relatively 

 easily recognized in the ash. 



The present book will be concerned only with techniques 

 belonging in classes 1, 2, 3a, Sb, and 4. They require little or 

 nothing in excess of the apparatus found in any reasonably 

 well-equipped laboratory of histology. 



cine (2d ed.; Baltimore: Williams & Wilkins, 1948); and Kurbatov, J. D., 

 and Pool, M. L.: Chem. Rev., 32:231, 1943. 



5. Policard, A., and Okkels, H.: Anat. Rec., 44:349, 1930; Scott, G. H.: 

 Protoplasma, 20:133, 1933, and Am. J. Anat., 53:243, 1933; Policard, A.: 

 Compt. rend. Assoc, anat., 29:463, 1934; Gage, S. H.: Stain Technol., 

 13:25, 1938; and Scott, G. H.: Biol. Symp., 10:277, 1943. 



