80 MEDULLA 



and finally brown, with the formation of an insoluble brownish 

 precipitate. Blood according to Maiweg 422 stabilizes epineph- 

 rine so that despite its alkalinity (pH 7.4) epinephrine is 

 not as rapidly destroyed as might be anticipated from its re- 

 action in aqueous solution. In the animal body, indeed, a 

 number of substances are present (glutathione, cysteine, as- 

 corbic acid and other reducing agents) which prevent the ir- 

 reversible oxidation of epinephrine and account for its pharma- 

 cological effects obtained at points distant from the site of its 

 injection. 666 



Epinephrine, like catechol, when oxidized is probably first 

 converted to an ortho-quinone. This quinone is destroyed 

 with such extreme rapidity that it is impossible to form an 

 oxidation-reduction system with epinephrine. 29 



Epinephrine forms relatively few stable salts. The hydro- 

 chloride which is the salt of commerce has already been men- 

 tioned. Boric acid forms a stable complex, C1SH27O11N2B3, 

 freely soluble in water. This complex is claimed not to be 

 decomposed by alkalies. A dibenzoyl derivative of epineph- 

 rine and a chlorbenzoyl derivative have also been described. 34 



COLORIMETRIC ANALYSIS 



The numerous reactions by which epinephrine forms colored 

 solutions has led to their utilization for its colorimetric analysis. 

 These methods for determining epinephrine are limited in 

 their applicability due chiefly to their non-specificity. Other 

 catechol derivatives as well as certain reducing substances also 

 give the same color reactions so that their presence in the solu- 

 tions to be tested lead to erroneously high results. Only the 

 most widely used methods will be discussed here. 



The green coloration produced by epinephrine or other 

 catechol derivatives when reacting with ferric chloride has 

 been used at times for their colorimetric determination. The 

 reaction is very sensitive to pH changes and gives unsatisfac- 

 tory results. According to most recent studies, the Vulpian 



