200 THE HOUSE FLY—DISEASE CARRIER 
upon the manure itself? Will it destroy its qualities 
and render it less valuable as a fertilizer? The ideal 
treatment would be to kill the fly larvae and make the 
manure more valuable, if that were possible. Finding 
that the use of iron sulphate seemed practical, as just 
pointed out, Forbes consulted a competent chemist, and 
received a reply from which he quotes as follows in a 
letter recently received by the writer: 
“A great deal of work has been done by German 
and French investigators in using sulphate of iron as 
a fertilizer. On going over this work carefully, we 
cannot find that sulphate of iron has ever proven in¬ 
jurious to the soil. On the contrary, its use gave very 
beneficial results in practically all cases. When sul¬ 
phate of iron is added to manure it will rarely, if ever, 
reach the soil; this for the reason that it will be con¬ 
verted either into ammonium iron compounds or de¬ 
composed into its elements. We have used as high as 
one hundred pounds of sulphate of iron to one square 
rod without rendering the ground sterile.” 
Professor Forbes goes on to state that his corre¬ 
spondent added that sulphate of iron is now being used 
in Florida by some of the most progressive orange 
growers and that very many carloads of it were shipped 
into that State during the summer of 1910. Further, 
that the orange growers of California are also buying 
it in large quantities. His correspondent concludes by 
stating that the small amount of sulphate of iron neces¬ 
sary for the extermination of flies will not have a dele¬ 
terious effect upon the soil. 
