SPECIAL TOXICOLOGICAL TESTS 277 



which they yield are freer from extraneous impurities, and also 

 because the residue which is injected into the frog (dissolved in the 

 water) represents the alkaloid and not its chloride. Should, 

 however, the evaporated acidulous extract be used for making the 

 frog test, then the check test should be made with the correspond- 

 ing pure alkaloidal salt. 



If the inoculated frog shows no marked symptoms of poisoning 

 in the course of 3 or 4 hr., it is very likely that the residue under sus- 

 picion does not contain any very poisonous substance. The pri- 

 mary object of the tests is to ascertain whether or not dangerously 

 toxic substances (alkaloids) are present in foods, and not for the 

 purpose of determining the identity of the alkaloid nor to demon- 

 strate the presence of comparatively nontoxic alkaloids. 



