CHAPTER XVIII 



RELATION TO DELETERIOUS CHEMICAL 



AGENTS 



A LARGE number of water-soluble chemical substances 

 are injurious to all living protoplasm at concentrations 

 considerably below the osmotic equivalent of the cell-sap. 

 Such injurious substances are poisons, or toxic agents. 

 These may act directly or indirectly upon the protoplasm, 

 and the inference is that the action is ultimately chemical. 

 The dilution of a deleterious agent often results in stimu- 

 lation, whilst at still further dilution this effect also 

 disappears. 



There is at present very incomplete knowledge of toxic 

 action; yet many advances have been made within the 

 past quarter-century. These advances have served to in- 

 crease knowledge generally, and in agricultural lines they 

 have been important in the study of soils, bacteriology, 

 plant pathology, and entomology. The results have been 

 utilized in the interpretation of experiments with fertiliz- 

 ers, in improving methods of disinfection or purification of 

 water-supplies, in the protection of plants against insect 

 pests and fungous diseases, and in various other ways to 

 which subsequently subsidiary reference may be made. 



263. General relations to poisons. - Toxic agents may 

 be general or specific poisons. Specific poisons are as yet 



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