116 Microscopic Histochemistry 



colored end-products. Only two examples will be quoted to 

 give an idea of the nature of the new tests: 



1. Amino groups of the protein are condensed with amino- 

 benzaldehyde; the aromatic amino group of the resulting 

 SchiflF's base can be diazotized and coupled with napthol. 



2. Phenolic groups of the protein are condensed with dini- 

 trochlorobenzene;^^ the nitro groups are reduced to amino 

 groups and the latter coupled with a diazonium salt. 



In both cases the final product will be an intensely colored 

 azo dye. Theoretically, this approach is sound and can be 

 expected to give excellent results. 



Antigens 



The microscopic localization of antigens in tissue sections 

 is one of the newest and most promising fields of histochem- 

 istry. 



The histochemical localization of antigens depends on the 

 fact that it is possible to introduce various chemical groups 

 into proteins without greatly changing their immunological 

 properties.^^^^ If an antibody is coupled, e.g., with tetrazo- 

 tized benzidine-R-salt conjugate, a red azoprotein is obtained 

 which will be selectively adsorbed to the original antigen. 

 This method has been used for in vitro aggulutination stud- 

 ies.^^ Unfortunately, the shade of the azoprotein cannot be 

 made dark enough to produce a satisfactory color contrast in 

 combination with the appropriate antigen in tissue sections,. 



In 1941 Coons and associates developed a much more sen- 

 sitive method by coupling antibodies with anthryl isocy- 



19. Bost, R. W., and Nicholson, F.: J. Am. Chem. Soc, 57:2368, 1935. 



20. Landsteiner, K., and Lampl, H.: Biochem. Ztschr., 86:343, 1918. 



21. Heidelberger, M., and Kendall, F. E.: Science, 72:252, 1930. 



22. Heidelberger, M., Kendall, F. E., and Soo Hoo, C. M.: J. Exper. 

 Med., 58:137, 1933. 



23. Reiner, L.: Science, 72:483, 1930; Heidelberger, M., and Kendall, 

 F. E.: J. Exper. Med., 59:579, 1934. 



24. Marrack, J.: Nature, 133:292, 1934. 



