Organic Substances 115 



aldehyde (vanillin, furfural, etc.) added, gives with trypto- 

 phane at 60°— 65° C. a fairly intense but unstable purple-red 

 color (Romieu's reaction^^). 



6. Ehrlich's p-dimethylaminobenzaldehyde reagent^^* ^^ 

 condenses with a number of phenols, amines, pyrrole and 

 indole derivatives^^ to give reddish and bluish dyes of un- 

 known constitution. 



7. a-amino acids give, when boiled with a 0.2-0.5 per cent 

 solution of ninhydrin ( triketohydrindene hydrate), a blue 

 coloration.^* This method works only with tissues not too thor- 

 oughly fixed and unembedded. The color of the reaction has 

 a great tendency to diffuse. 



8. Alloxan in aqueous or alcoholic solutions gives a red 

 color with a-amino acids. ^^ The shade is so pale as to make 

 the reaction worthless for histochemical purposes. 



9. Voss^^ recommends the use of o-diacetylbenzene (10 

 per cent in 70 per cent alcohol ) as a reagent for amino acids 

 and proteins ( bluish-red color ) . 



Reactions 6-9, being specific for NH2 groups, will be nega- 

 tive after formalin fixation.^^' ^'^ 



An entirely new avenue for the histochemical investigation 

 of protein substances is proposed by Danielli.^^ He recom- 

 mends the application of a number of important condensa- 

 tion reactions of organic chemistry so modified as to yield 



10. Romieu, M.: Compt. rend. Acad, sc, 180:875, 1925; Blanchetiere, A.: 

 Compt. rend. Acad, sc, 180:2072, 1925; Blanchetiere, A., and Romieu, M.: 

 Compt. rend. Soc. de bioL, 107:1127, 1931. 



11. Ehrlich, P.: Med. V^chnschr., p. 151, 1901. 



12. Lison, L.: Histochimie animale (Paris, 1936), p. 160. 



13. Rohde, E.: Ztschr. f. physiol. Chem., 44:161, 1905; Fleig, M. C: 

 Bull. soc. chim. France, 4th ser., 3:1038, 1908. 



14. Ruhemann, S.: J. Chem. Soc, Tr., 97:2025, 1910; Berg, W.; Klin. 

 Wchnschr., 2:1757, 1923. 



15. Krasser, F.: Monatschr. f. Chem., 7:673, 1886; Hurtley, V^. H., and 

 Wootton, V^. O.: J. Chem. Soc, Tr., 99:288, 1911; Giroud, A.: Protoplasma, 

 7:72, 1929. 



16. Voss, H.: Ztschr. f. mikr.-anat. Forsch., 49:51, 1940. 



17. Duliere, W. L.: Biochem. J., 30:770, 1936. 



18. DanielH, J. F.: Cold Spring Harbor Symp. Quant. Biol., 14:32, 1950. 



