50 Effect of Zinc Compounds 



A few tests on yeasts made by Javillier showed that with vegetative 

 yeasts zinc has a specific action, a consistent increase occurring in the 

 amount of yeast formed and in the amount of sugar consumed as the 

 quantity of zinc increased from 1/10,000,0001/10,000. With 

 ferment yeast, however, zinc exerted no appreciable action. These 

 results lend force to the conclusion of Richards (1897) who carried out 

 experiments on fungi with various nutritive media with the addition 

 of certain salts of zinc, nickel, manganese, iron, &c. He considered 

 that his general results showed that the fact of a chemical stimulation 

 of certain metallic salts upon the growth of fungi is established, although 

 it must not be considered without further investigations that all fungi 

 react in the same degree to the same reagent. 



Conclusion. 



As matters stand at the present day, it appears that it is still un- 

 certain whether higher plants grown in water cultures are susceptible 

 to stimulation by zinc salts. If a stimulus does exist, it must be at 

 exceedingly great dilutions, but further evidence is needed. In soil 

 cultures, however, the fact of increased growth seems to be more firmly 

 established, certain species responding to zinc salts when used as 

 manure, though no increase has been obtained with other species. It 

 must always be remembered that the action may be an indirect one. 

 The soil is very complex in its -constitution, and it is impossible to 

 determine the exact action of the added poison upon it, so that a 

 stimulating effect need not necessarily be due to a direct action of a 

 substance upon the plant, but it may be the result of more favourable 

 conditions for life induced by the action of the substance upon the soil. 



Among the fungi the stimulation of Aspergillus niger by minute 

 traces of zinc compounds seems to be well proved, though again it does 

 not necessarily follow that all fungi will react in the same way to zinc. 



