INTRODUCTION 



Histochemistry is a borderline field between histology and 

 analytical chemistry or biochemistry. Its subject matter is the 

 identification and localization of chemical substances in the 

 tissues on a cytological scale. In the present book the term 

 will be used in a more restricted sense to include only those 

 methods in which the identifying chemical reaction is ob- 

 served directly through the microscope, in tissues of which 

 the architecture is not grossly altered. This definition will 

 eliminate at once two other important ways of approach: 

 ( 1 ) those in which certain morphological structures ( nuclei, 

 mitochondria, etc.) are first separated by physical means, 

 such as differential solubility or centrifugation, and are then 

 analyzed chemically and (2) the ingenious statistical meth- 

 ods developed by Linderstr0m-Lang^ and his school. "Cyto- 

 chemistry" is often used as a synonym; however, it should 

 be reserved for the study of the chemical organization of the 

 cell in general.^ 



Histochemistry is a young science, although a few histo- 

 chemical reactions have been known for over seventy years 

 (iodine reaction for starch;^ Prussian blue reaction for iron*). 

 Actually, probably most of the staining techniques described 

 since the earliest days are based on some chemical or physi- 

 cochemical interaction between dye and tissue; however, 

 they cannot be called "histochemical" for two reasons: (1) 

 the underlying chemical reactions are not understood, and 

 (2) their results, valuable as they may be for the differenti- 

 ation of various morphological structures, do not convey any 

 information about their chemical constitution. 



1. Lmderstr0m-Lang, K.: Bull. New York Acad. Med., 15:719, 1939. 



2. Dick, A. T.: Australian Chem. Inst. J. & Proc, 15:294, 1948. 



3. Caventou, J. B.: Ann. de chim. et phys., 31:337, 1826. 



4. Perls, M.: Virchows Arch. f. path. Anat., 39:42, 1867. 



