Bitter Pit in Apples, 399 



Copper sulphate 1 per 1,000,000, and citric acid 10 per 

 1,000,000, From slight superficial browning to pits 1 mm, deep. 



The nature of toxicity. 



It is generally assumed that the toxicity of the heavy metals 

 is due to their combining with the proteids of protoplasm, and 

 that they are toxic in great dilution because the protoplasm has 

 the power of absorbing and accumulating them in greater con- 

 centration than in the liquid outside. To some extent this is 

 true, but nevertheless the foregoing experiments have shown 

 that pulp cells poisoned by mercuric chloride may not contain 

 this poison in a concentration of more than 1 in 30 to 100 mil- 

 lions, and possibly even less. It must be remembered, however, 

 that the adult pulp cells of apples have only a thin layer of 

 protoplasm, and that if this is killed at any point, however small, 

 the death of the whole cell follows for physical reasons, in much 

 the same way that a balloon collapses when pricked by a pin. 



Certain cases of toxicity appear to be due to the removal by 

 displacement or ionic interchange of the kations of metallic 

 physiological salts present in the cell, such as calcium nucleo- 

 proteate. Thus Loew^ has shown that various substances which 

 precipate calcium (sodium fluoride, potassium oxalate) are poi- 

 sonous to Spirngi/ra, and apparently act by removing the 

 calcium from the nucleo-protein acids of the nucleus. 



Similarly Loeb^ showed that sodium chloride was poisonous to 

 the eggs of a certain fish, but not when calcium was present in 

 the external. solution, and according to Loew^ this action would 

 be due to the removal of calcium in the one case, and its non- 

 removal in the other. It is possible that the feebly poisonous 

 action of potassium salts might be due to their displacing cal- 

 cium or magnesium from the protoplasm of the pulp cells of 

 apples, but if so it is diflicult to understand why the addition 

 of a potassium salt to a magnesium one does not increase the 

 poisonous action, but if anything has the reverse effect. It may 

 be that since magnesium and potassium are present inside the 



1 Bull. Coll. Agric, Tokyo., Imp. Univ., vii. 190(j., p. IS. 



2 Arch. f. f. ges. Physiol. 107, p, 252., 1905. 



3 See also OsVjorne, Froc. Physiol. Soc. xxxiii, 1905, p. 1. and 1906, xxxiv., p. 84. 



