HOW DOES THE ARSENIC ACT 123 



4,000,000,000. Although Russell states that it is not as toxic in 

 soil as in water, Darbishire and Russell found it to be toxic in soils, 

 and they failed to get a stimulating influence with it. Monte- 

 matini has noted a stimulation with copper sulphate when used in 

 dilute solutions. This, however, may have been due to the anipn 

 and not to the cation, as sulphates do stimulate plants by their action 

 on insoluble constituents of the soil. The same interpretation could 

 be placed upon the results obtained by Lipman and Wilson and also 

 those reported by Voelcker in which they noted a stimulation with 

 copper salts. Clark and Gage have found that very dilute solutions 

 of copper have an invigorating influence upon bacterial activity. In 

 order that the stimulation may be noted the copper must be present 

 in small quantities. Jackson found that 1 part of copper sulphate 

 in 50,000 parts of water kill Bacillus coli and Bacillus typhosus. 

 Kellermann and Beckwith found that the common saprophytic 

 bacteria are more resistant to copper than is B. coli. There is con- 

 siderable evidence that copper stimulates the ammonifying and 

 nitrifying organisms of the soil, but these results show the nitrogen- 

 fixing organisms of the soil to be very sensitive to copper, and if it 

 is to act as a stimulant it must be in extremely dilute solutions. The 

 toxicity of the copper in the Paris green is great enough in the 

 dilution of 10 parts in 1,000,000 to offset the great stimulating 

 influence of the arsenic in combination with it. 



The marked stimulating influence noted where the arsenic trisul- 

 phid is used is very probably due to the stimulating action of both 

 the arsenic and sulphur. Demolon attributed much of the fertilizing 

 action of sulphur to its action upon bacteria, and Vogel found that 

 sulphur decidedly increased the activity of the nitrogen-fixing organ- 

 isms. The results which Russell and Hutchinson obtained with 

 calcium sulphid are interesting in this connection. They found that 

 after thirty days there were five times as many organisms in a soil 

 to which calcium sulphid had been added as in an untreated soil, and 

 the yield of ammonia and nitrates in the same length of time was 

 one-third greater in the treated soil than in the untreated soil. This 

 in turn reacts upon the crop harvested, as shown by Shedd. 



The first part of the curve for zinc arsenite nearly coincides with 

 that of sodium arsenate, save that zinc arsenite stimulates in greater 

 concentrations than does sodium arsenate. This is partly due to 

 the difference in solubility of the two compounds, but there is 

 another factor that the zinc also acts as a stimulant. Latham 

 found that small quantities of zinc stimulated algse. The same 

 results have been obtained by Silberberg in working with higher 

 plants. Ehrenberg concludes that zinc salts are always toxic when 

 the action is simply on the plant, but that they may lead to increased 

 growth through some indirect action on the soil. He found that zinc 

 stimulated plant growth in soils, but when the soil was sterilized the 



