376 Alfred J. Ewavt : 



metallic poisons as mercury in greater concentration than in a 

 dilute solution presented to them. 



Additional evidence was obtained in the following way : — 

 Two cubic centimetres of the pulp of two of the above apples 

 were removed, and, after washing, placed in one litre of distilled 

 water with a prepared Rome Beauty floating on top. The 

 liquid was gently stirred daily, and after one week the apple 

 was removed. The prepared spots already showed signs of 

 poisoning, and after one week in air developed from a super- 

 ficial browning to pits 1 millimetre deep. The 2 centimetres of 

 poisoned pulp were then crushed, and kept in contact with a 

 clean strip of pure copper for one week. No trace of mercury 

 was deposited. The pulp was then treated with sulphuric 

 acid, nearly neutralised, and kept in contact with a clean strip 

 of copper for one week. A slight but distinct stain of mercury 

 was formed, volatilising on heating, but not in sufficient quantity 

 to be accurately weighable. Judging from a comparative test 

 the total amount was a very small fraction of a milligram. 



It follows therefore that the pulp cells do fix mercury, and 

 that the mercury is liberated again by treatment with sulphuric 

 acid. The poison that diffused from the dead pulp would at first 

 be merely mercuric chloride in solution. Since the concentration 

 outside was 388 milligrams per litre, not more than 0.7 of a 

 milligram of mercuric chloride could have been present in solu- 

 tion in the poisoned pulp. This would produce at the most 

 a concentration of 7 in 10,000,000 in the litre of water in which 

 the prepared apple lay, and probably considerably less, since the 

 poison as it exudes is being absorbed by the second apple. The 

 special interest of this observation lies in the fact that if its 

 rationale were not known, it might have led to the conclusion 

 that the dead pulp of one apple was able to communicate a 

 disease to the second one. Instances of oligodynamic poi- 

 soning may be much commoner than is generally supposed, 

 and it is in fact possible that certain other diseases of 

 plants and even animals may directly or indirectly have 

 a similar origin. All that is necessary is to have sen- 

 sitive cells capable of absorbing or accumulating very minute 

 traces of poison. If these cells were in a growing tissue 

 the symptom of poisoning might be an increased or abnormal 



