42 



Mr. H. Onslow. 



(c) Properties — 



Experiment I: The Influence of Hydrogen Peroxide and of the Reaction of 

 the Ferment Fluid. — The ferment fluid was added to each tube. 





Appearance after 12 hours. 





Chromogen added. 







Remarks. 





Without H 2 2 . 



With H = 0.,. 





None 







Reaction faintly alkaline. 



Tyrosine 







Boiled. 





+ + 



Reaction faintly alkaline. 









Reaction strongly alkaline. 









Reaction neutral. 









Reaction acid. 



+ + indicates strong reaction. 

 + indicates positive reaction. 

 — indicates no change. 



From this experiment it appears that the ferment fluid lacks both a 

 chromogen and a peroxide, for only when both these naturally occurring 

 substances are replaced by tyrosine and hydrogen peroxide can oxidation 

 take place ; in other words, the ferment fluid contains only the peroxidase 

 constituent of the pigment-producing mechanism. As a matter of fact, 

 in later experiments when more practice had been obtained in extracting 

 the ferment fluid, and when more care was taken to use the material as 

 fresh as possible, a small amount of natural chromogen and peroxide was 

 sometimes extracted. This was indicated by the formation of a dark grey 

 ring in those tubes which contained either the chromogen or the peroxide, 

 as well as in those which contained the ferment fluid alone. Tubes with 

 a neutral reaction were only faintly grey after 12 hours, but subsequently 

 they began to darken. Tubes with an acid reaction, however, remained 

 permanently colourless. If alkali was present in excess, the reaction could 

 not take place, nor did the tube containing the boiled ferment fluid show 

 any sign of darkening. The peroxidase was found to be precipitated on 

 saturating the fluid extract with ammonium sulphate, or on the addition of 

 an excess of alcohol. 



Experiment II: The Inhibitory Effect of Ferrous Sulphate. — The ferment 

 fluid (prepared as previously, see pp. 40 and 41) was added to each tube, also 

 tyrosine and hydrogen peroxide in the same quantities as in Experiment I. 



