107 



tion. Three or four drops of a coffee-bean extract showing a very 

 high oxidase activity were added to lo c.c. of fresh lemon 

 juice, with the result that the oxidase action was inhibited, 

 but immediately after neutralization the oxidase caused a faintly 

 positive test. This same experiment was repeated, using 9.25 

 c.c. of N/5 acetic acid solution, the N/5 solution being used to 

 make the total acidity equal to that of the lemon juice and to 

 keep the total volume always the same (10 c.c), with the ad- 

 dition of distilled water and a few drops of coffee-bean extract 

 as before. To our surprise this apparently did not affect the 

 oxidase at all, for a very strong coloration was obtained with 

 guaiac tincture, etc. Then the experiment was repeated in 

 exactly the same manner upon mixtures containing 9.25 c.c. 

 of N/5 H2SO4, HCl, and citric acid solutions. The results were 

 the same in the three cases: the oxidase reaction was completely 

 inhibited and after neutralization wdth calcium carbonate or 

 potassium hydroxid, a faint bluish coloration of guaiacum was de- 

 tected in the citric acid test-tube. The rest were negative after 

 neutralization. The sulphuric acid mixture was neutralized with 

 calcium carbonate and divided into two portions, to one of which 

 fresh coffee extract was. added, to the other some fresh guaiac 

 tincture; no bluing was produced in either case, nor was it ob- 

 tained in several repetitions of the experiment. 



To determine more exactly the influence of different acids 

 upon the bluing of guaiacum by the oxidase of the coffee-bean, a 

 series of experiments were made in the manner already described. 

 In all cases the results obtained were consistent and showed 

 the inhibiting effect was traceable to the activity of the hydro- 

 gen ions from the acids in aqueous solution. We conclude, 

 therefore, that the failure to find oxidases in most plant juices, 

 when the acidity is greater per 10 c.c. than that equal to the 

 alkalinity of 0.6 to 0.8 c.c. of N/io KOH solution, is due to the 

 effect of the different acids upon the peroxidases, etc., and this 

 influence is probably not specific for the acids, but depends 

 upon their dissociation and consequent yield of hydrogen ions. In 

 the following table we indicate the known comparative accelerat- 

 ing effects of these common acids upon the inversion of sucrose. 



