B'iftcr Pit 845 



or nearly so. instead of turning brown. If fresli apple pulp is 

 pounded up with 0.5 to 2.5 % solutions of sodium chloride, it does 

 not turn brown, although the cells are completely killed. The pulp 

 ^ivee even after some hours a faint blue with guiacuiii. a strong 

 one with guiacum and hydrogen peroxide, and a fairly i-apid 

 reaction with ursol tartrate. Salt, therefore, prevents the oxida- 

 tion of tannic acid by apple oxidase without destroying the latter. 

 and it is a sensitiser to the oxidase action on guiacum, which 

 normally only turns l)lue with guiacixm in the i^resence of hydrogen 

 peroxide. I have already given specific instances of many similar 

 specific " antioxidase " and "sensitiser" reactions. ;ind have 

 shown that the presence of salt affects various of the colour reac- 

 tions of tannic acid, including its reaction with ferric chloride. 



Owing to the action of salt in preventing broAvning it is difficult 

 to determine its poisonous action. So far as can be judged by 

 microscopic examination of the cells beneath the prepared spots 

 where the salt solution is absorbed, it appears to belong to the 

 elass of almost non-poisonous salts as compared with mercury and 

 copper salts, and to be less poisonous than potassium salts. With 

 strong solutions osmotic injury is caused, but this is mainly con- 

 fined to the surfaces of the prepared spots. 



In regard to the statement that browni pits developed in apples 

 floated on distilled Avater beneath the prepared spots from which 

 the cuticle had been removed, I was fortunately able to examine 

 subsequently the apples in question and to see that not only the 

 cuticle but also the epidermis and hypodermis had lieen removed 

 right doAvn to the pulp tissue. The importance of not removing 

 these layers is that they form continuous layers of cells without air 

 spaces (except at the lenticels), and hence prevent the invasion of 

 micro-organisms, which takes place very rapidly in water, particu- 

 larly if any of the pulp cells have been injured or cut, and is soon 

 followed by an invasion of fungal hyphae. 



The browning of peeled pulp floated in distilled water is usually 

 due to the action of micro-organisms. They can l)e seen in a few 

 hours, and if the water is previously sterilised, all ])ossible .anti- 

 septic precautions taken and the peeling done witli a sliarp razoi-, 

 the browning of the pulp is very slow. Peeled pulp will remain 

 fresh and living under kerosene for as long as 2 to 3 weeks, show- 

 ing that the death of the pulp is not due to asphyxiation by diow ii- 

 ing. In fact, apples remain living for some Aveeks in an atmo- 

 sphere of nitrogen or hydrogen. 



