ALDEHYDES AS CHROMOGENIC REAGENTS 105 



4. Sections are washed in two changes of 0.1 N hydrochloric acid for 3 

 or 4 minutes, and transferred to 



5. A nitrous acid solution obtained by dissolving 0.5 gram of sodium 

 nitrite in 100 milliliters 0.1 N hydrochloric acid kept at 0° C. The sec- 

 tions are kept in this solution for 5 minutes to diazotise the amino groups. 



6. The sections are transferred to an alkaline solution of a phenol or a 

 solution of an aromatic amine, e.g., H acid or a-naphthol or /3-naphthyla- 

 mine. After 15 minutes in this solution coupling with the diazotised sec- 

 tions should be complete. 



7. The sections are washed in tap water and mounted in balsam. 



Table VIII gives a list of some of the nitro reagents which are 

 usually available and indicates the groups of proteins for the 

 study of which they are particularly suitable. 



Aldehydes as Chromogenc Reagents 



A third family of compounds useful in the cytochemistry of 

 proteins are those containing two reactive groups, one of which 

 is an aldehyde group and the other of which may be any of a 



TABLE IX 



Aldehyde reagents under investigation for the cytochemistry of 

 and — NH 2 groups. 



-SH 



CHO 



CHO 



CHO 



o 



NH, 



CHO< 



>N0 2 





CHO^ >COCH 2 Br 



CHO 



>0-CO-CH 2 I 



+ 



+ 



+ 



CHO 



o 



H • CO • CH 2 I 



SH 



+ 



+ 



+ 



