92 HEWSON SWIFT 



has replaced pyronin with an aqueous solution of the more dependable toluidine blue 

 O {CI. 925). 



Gallocyanine-chrome alum: Stock solution:*' chrome alum (purified), 5 g. in 100 

 ml. water, with 0.15 g. gallocyanine, boiled gently for 5 minutes, cooled, and filtered. 

 The pH should be 1.64. The solution slowly deteriorates, and should not be used for 

 more than 4 weeks. A more intense stain may be obtained by increasing the pH, but 

 this also increases the extent of nonspecific staining. Treat slides for 48 hours at room 

 temperature. PNA and DNA are stained a blue-purple (absorption maximum about 

 500 m/x). There may be some nonspecific background staining. ^'-^^ 



