2 20 BOTANICAL GAZETTE [march 



This view is substantiated by the fact that when the concentration 

 of ferrous chloride is reduced, oxygen absorption is reduced pro- 

 portionally (table VI). If we subtract 1.45 cm. (mercury rise 

 for pyrogallol and ferrous chloride) from 1.79 cm. (mercury rise 

 for bark, pyrogallol, and ferrous chloride), we have 0.34 cm. for 

 the oxidase activity of the bark in the presence of the ferrous 

 chloride as compared with 1.00 cm. for the oxidase activity of 

 bark and pyrogallol in the absence of ferrous chloride. Apparently 

 ferrous chloride retards oxidase activity just as the other chlorides 

 do, and the increased absorption of oxygen in the presence of 

 ferrous chloride is due to the action of ferrous chloride itself in 

 absorbing oxygen. Oxidation is increased by 0.002 N manganese 

 chloride. This is in accord with the results of Bertrand (5 and 

 others. In a concentration of 0.1 N it inhibits oxidation just as 

 do the other chlorides. 



The use of precipitated oxidase shows that chlorides have a 

 depressing effect on oxidation, even under conditions which elimi- 

 nate many of the substances present in the bark powder. No 

 investigation has been made of the effect of these substances on 

 the reaction, but they probably complicate it. 



The results with the chlorides are in accord with the work 

 of Ewart, who found that dilute solutions of potassium 

 chloride and sodium chloride prevent the browning of slices 

 of apples. Ewart's further conclusion, however, that the chlo- 

 rides act as sensitizers to oxidation, or Alsberg's idea that 

 chlorine plays an important part in the bluing of guaiacum by 

 the chlorides of metals, are scarcely borne out by our observations 

 that chlorides in general depress oxidase activity. It should be 

 noted, however, that the results of those investigators were 

 based upon color reactions, while ours were based upon oxygen 

 absorption. 



It is interesting to note that the chlorides which retard the 

 combustion of tobacco at high temperatures have a similar effect 

 in depressing oxidase activity. Kraybill (21) has suggested that 

 the chlorides may have a negative catalytic action in the case of 

 the combustion of tobacco. It would be interesting to know 

 how the chlorides affect other oxidation processes. 



