1914] Paul E. Howe 271 



A study^ o£ the factors which may interfere witli the reaction 

 has shown that the Solutions involved must be neutral. A more 

 detailed consideration^ of the factors which influence the produc- 

 tion of the blue color has shown that the addition of alkali to the 

 Solution to be tested, before the addition of the triketohydrindene 

 hydrate, interferes with the test; the addition of alkali after the 

 color has developed does not dissipate the color, Acids, even com- 

 paratively weak organic acids, not only hinder the reaction but 

 decolorize the Solution after the color has developed. The effect 

 of the higher fatty acids depends upon whether they are saturated 

 or unsaturated, in the latter case they interfere. The effect of 

 electrolytes varies with the cation and is independent of the anion. 

 In some cases (sodium and potassium) there is a precipitation of 

 the colloidal color substance, in other cases (calcium and cadmium) 

 the effect is a change in the intensity of the color without precipita- 

 tion, while in still others (ammonium and magnesium) there is no 

 appreciable change. 



A few observations upon the biological activity of triketohy- 

 drindene hydrate have shown that following hypodermic injection 

 (frogs) the tissues are stained blue and cardiac paralysis results. 

 The fatal dose for frogs is 0.002-0.005 gm. and death may ensue 

 without the appearance of the substance in the urine. It is an irri- 

 tant poison, a 1/1024 percent Solution causing a transitory burning 

 Sensation when dropped on the eye. It is not a general proto- 

 plasmic poison, for the growth of yeast is hardly inhibited. 



From the evidence cited it appears that triketohydrindene hy- 

 drate (ninhydrin) is a very satisfactory test for the presence of 

 Compounds having free amino and carboxyl groups attached to 

 aliphatic radicals — amino acids, peptone, protein, etc. The typical 

 blue color may result under other conditions than in the presence of 

 amino acids and the related substances. When the reagent is used 

 under the conditions ordinarily prescribed — in a neutral Solution, 

 distilled water with a negative or very low salt content — a positive 

 test results only in the presence of amino acids. 



Biochcmical Laboratory of Columbia University, 

 College of Physicians and Surgeons, New York 



8 Ruhemann: Loc. cit.; Abderhalden and Schmidt: Loc. cit. 

 * Halle, Loewenstein and Pribram : Loc. cit. 



