14 ANTAGONISM 



but to a poisonous or toxic effect of the latter upon the proto- 

 plasm. Two compounds, however, which separately exert such 

 a harmful effect can often, if mingled in certain proportions, 

 provide a solution which produces no plasmotysis and is not 

 poisonous. 



For example, if germinating zoospores of Vaiichcria (cf. p. 217) 

 are placed in weak solutions of sodium chloride (ranging from 

 0'0937 to o"ooi M), plasmolysis ensues more or less rapidly (in 

 the case of the weaker solutions only after an interval of a day 

 or more). If, however, calcium chloride is added to the salt 

 solution in the proportion of one molecule of the former to one 

 hundred of the latter, the young plants of Vaucheria can be 

 subjected to strengths up to as much as o'l M without any 

 contraction of the cell-contents. Indirectly the same effects 

 can be observed by studying the growth and duration of life 

 of young plants of the same Alga in the different solutions : 

 in sodium chloride alone or calcium chloride alone there is prac- 

 tically no growth and death soon takes place ; whilst in a mixture 

 of the two in the proportions mentioned above, growth is as 

 vigorous, and the plants remain alive as long, as in glass-distilled ^ 

 water or in much diluted sea-water. 



Similar observations can be made on the development of 

 the root-system of Wheat -seedlings, although these are not so 

 sensitive to the poisonous solutions. In the same way potassium 

 chloride and magnesium chloride are toxic when used separately, 

 though when mixed in suitable proportions the poisonous effect 

 largely disappears. Analogous results have been obtained with 

 animals and animal-cells. 



It is not only the chlorides that give such results, for similar 

 effects have been obtained with nitrates, sulphates, etc. All 

 these compounds are employed in such dilute solutions that 

 dissociation of the molecules into ions will have taken place. 

 Since in the different experiments much the same amount of 

 chloride is present, the striking results obtained must be due 

 to some effect of the metallic ions, probably upon the proteins 

 of the plasmatic membrane. The prevention of the poisonous 

 action of one ion by one or more other ions is spoken of as 



1 Ordinary distilled water often contains traces of copper, etc., which 

 are exceedingly harmful to most vegetable organisms. 



