Organic Substances 123 



tions. The slides are fixed in formaldehyde vapor and subse- 

 quently treated with various reagents. It will be observed 

 that phenol, tyrosine, catechol, and hydroquinone lose their 

 azo-coupling reactions after this treatment (or produce azo 

 dyes so pale as to be indistinguishable from the shade of the 

 control marks ) ; the indophenol reaction of phenol and cate- 

 chol is completely abolished. The chromaflBn and argentaflBn 

 reactions of catechol and hydroquinone are greatly weak- 

 ened. If formalin fixation is followed by treatment with 5 per 

 cent potassium dichromate for 24 hours, the argentafiin reac- 

 tion of these diphenols is abolished. On the other hand, 

 resorcinol and phloroglucinol fully retain their azo-coupling 

 ability and will produce azo dyes of brilliant shades; their in- 

 dophenol reaction also remains unimpaired. They will show 

 an intense chromafiin and argentafiin reaction; the latter is 

 resistant to treatment with dichromate. 



These observations are of great importance, as they show 

 that in the case of phenolic substances the results of test-tube 

 experiments cannot be used for their identification in fixed 

 tissues. 



Adrenalin 



The adrenal medulla reduces alkaline silver solutions,^^ 

 stains brown with dichromates,^^ gives azo dyes (of an in- 

 conspicuous ochre-yellow shade, suggestive of catechol de- 

 rivatives) with diazonium compounds, shows a definite in- 

 dophenol reaction and a greenish staining with ferric chloride 

 solutions. There can be little doubt that all these reactions 

 are due to the presence of adrenalin. However, they can be 

 obtained with fresh material only; once the tissue is fixed 

 either in formalin or in alcohol, they become negative. With 

 alcohol, loss of reactivity is probably due to extraction of 

 adrenalin from the tissue; with formalin, chemical changes 

 induced in the molecule must be held responsible for the 

 negative reactions. 



For the histochemical demonstration of adrenalin, the tis- 



18. Henle, J.: Ztschr. f. ration. Med., 24:142, 1865. 



