394 Alfred J. Eivart : 



areas on the paler shaded side may still show faint but distinct 

 signs of poisoning, while those on the red side are quite unaf- 

 fected. This greater resistance of the superficial pulp cells on 

 the exposed side to poison is not due to the cuticle or bloom 

 since they haA-e been removed prior to the test. There is no ]Der- 

 ceptible difference in the thickness of the cell walls, but the 

 pulp cells in some cases at least were slightly smaller on the 

 exposed side, and hence presumably contained a relatively 

 greater bulk of protoplasm to be poisoned. It can often be 

 noticed that when an apple is strongly exposed on one side, and 

 shaded on the other, it develops a greater radius on the shaded 

 side. Apparently this is partly, at least, due to the cells becom- 

 ing larger on that side. Dr. White noticed that bitter pit was 

 commoner on the shady side of the fruit or tree than on the 

 exposed side, and suggested that the moisture would persist 

 longer on the shaded side and so favour the entry of spray 

 poisons. Apparently, however, the exposed side of an apple 

 actually retains a greater resistance to poisons than does the 

 shaded side. 



The influence of ionization and of tlie 

 respective ions. 



In the case of all compounds which undergo dissociation when 

 dissolved in water, the poisonous action is the result of the 

 joint action and non-action of the different ions and of the 

 undissociated molecules of the compound. A salt may be poi- 

 sonous on account of either the basic or the acidic radic]e coujpos- 

 ing it being poisonous, or both of them\ Further, if one of the ions 

 is much more poisonous than the other, or than the undisso- 

 ciated salt, then increasing dilution, since it increases the rela- 

 tive omount of dissociation, Avill not produce a decreased poison- 

 ous action in direct but in decreasing ratio to the dilution. To 

 some extent this may explain the excessive dilutions at which 

 such salts as mercury, copper, etc., may remain poisonous. 

 More exact comparisons can only be made by calculating the 

 poisonous concentrations in terms of the molecular weights of the 



1 For literature see Pfeffer's Physioloify, vol. ii., p. 273. (En-;. Trans.) 



