318 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



risk is not greater than that of railway or steamship travel or many 

 other practices which are necessary. 



These remarks will apply also to the dangers accruing to animals from 

 this use of i)oJson. For, although we are informed that the annual loss 

 by Paris green of cows, sheep, and horses is something considerable, no 

 instance has come under our personal observation. 



As to the accumulation of the arsenic in the soil, in sufficient quantity 

 to prove injurious to plants, we cannot do better than to cite the inves- 

 tigations of Dr. WiUiam McMurtrie.* These investigations show — 



That, though arsenical compounds exert an injurious influence upon vegetation, yet 

 this is without effect until the qtiantity present reaches, for Paris green, ahout 900 

 pounds x^er acre ; for arsenite of potassa, about 400 pounds per acre. 



Thus, if all the arsenic were to remain in the soil no injurious effects 

 need be expected to follow within one hundred years. And when we 

 take into consideration the amount of arsenic which is removed from the 

 soil by drainage, an even greater time may be expected to elapse before 

 that event occurs. And w^e may reasonably expect that ere that time 

 the science of economic entomology will be so far advanced that a harm- 

 less substitute for arsenic will be known if there remains an occasion for 

 its use against this enemy of the cotton plant. 



Carholic acid. — Experiments conducted by Professor Willet and my- 

 self last season with carbolic acid gave results similar to those obtained 

 by Mr. Trelease. It was found in each case that where this substance 

 was used in sufficient quantities to destroy the worms it injured the cot- 

 ton plants greatly. 



Kerosene. — Although the different forms of coal-oil have been found 

 to be very valuable in many instances as insecticides, all of our efforts 

 to employ it against the cotton-worm have produced poor results. In 

 every case when a mixture of kerosene and water of sufficient strength 

 to destroy the worms has been applied to cotton, the plants have been 

 injured. 



The following experiment, suggested by the use made of kerosene 

 against the Eocky Mountain locust, was tried : A quantity of kerosene 

 was put into a pan ; all that would flow was then poured out, leaving 

 only a thin film over the bottom of the pan. A dozen cotton-worms 

 were then put into the pan. At the end of two minutes all were dead. 

 But the danger of injury to the cotton plant, and especially of knocking 

 off the bolls by any machine employed for jarring the worms from the 

 plants into receptacles containing coal-oil, will prevent the use of this 

 substance in this way. 



Pijrethrum. — The value as an insecticide of powder made from the 

 dried tlower-heads of different species of Fyrethrum,^ and sold under the 

 name of Persian Insect Powder, has long been known, but its expense 

 has prevented its general use except for insects infesting houses and 

 parasites upon doujestic animals. For the same reason, we neglected 

 to experiment with it on the cotton- worms, believing that, however effi- 

 cient it might be, its cost would prevent its use against insects infesting 

 field croi>s. But there has been introduced into Cahfornia a Dalmatian 

 species oi Pyretlirum [Pyretlirum cineranaejolium), from which a powder 

 equally as good as the imx>orted powder is made. And we have recently 

 learned, what is equally important, that this powder can be produced at 

 a price which will admit of its being used on field croi)s. The Califor- 

 nian powder is known as buhach. 



The most important peculiarity of i)owder made fi'om Fyrclhrnm is 

 that, although deadly to insects, it is harmless to man and domestic 



* Annual Report of tlie Department of Agriculture, 1875, pp. 144-147. 



