2 BULLETIN 259, U. S. DEPARTMENT OF AGRICULTURE. 



still present in its original quantity but that it had partly changed 

 its form and now existed to that extent as sodium arsenate, 1 a com- 

 pound, as previously indicated, quite different hi many of its proper- 

 ties from sodium arsenite. Fuller, 2 who independently discovered 

 the phenomenon in the laboratories of the Bureau of Animal Industry, 

 went further and showed that the change is essentially brought about 

 through the growth of microorganisms in the dipping baths, other 

 factors being relatively of little importance. 



After the appearance of Fuller's paper pressure of other work 

 prevented the obtaining of further knowledge along this line except 

 what could be gained from the routine examination of samples from 

 the field and an occasional desultory experiment. What was thus 

 learned, however, indicated that the matter was probably not yet 

 thoroughly understood and that at any rate practical studies should 

 certainly be undertaken on the progress of the phenomenon of oxida- 

 tion as it occurs in dipping vats in the field under varied conditions 

 of actual use. The relative efficacy of solutions of arsenite and 

 arsenate against ticks and their relative toxicity toward animals 

 dipped therein are subjects entirely beyond the scope of this paper, 

 but it is universally believed that sodium arsenite is a much more 

 powerful tickicide than sodium arsenate, though at the same time 

 more poisonous to cattle. It was clearly a matter of importance to 

 ascertain how rapidly a change from one form to the other might go 

 on in baths in actual use in the field, since such a change is necessarily 

 closely related to the regularity of action of a bath upon both ticks 

 and cattle. These field studies have, been continued during the past 

 two years. 



In the meantime further published work has appeared abroad. 

 Laws 3 in explanation of certain observations suggested that, in 

 addition to the oxidizing organisms already noted which change 

 arsenite to arsenate, there may also exist in some baths reducing 

 organisms which change arsenate back to arsenite. He also suggested 

 the use of some bactericide to prevent oxidation by preventing the 

 growth of the bacteria which cause it. Brunnich and Smith, 4 Wil- 

 liams, 5 and Holborow 6 have made some studies of the obvious ques- 

 tions presented. But the published work so far seems in general 

 hardly comprehensive enough to insure the drawing of sound prac- 

 tical conclusions, while in any event it is confined to certain foreign 

 countries where dipping practice as respects strength of dip and 



i Brunnich (Australian Association for the Advancement of Science, 1909, through Journal of Agricultural 

 Science, 1911, vol. 4, p. 177) appears to have been first to make this discovery. 



2 Bureau of Animal industry Circular 182, Nov. 9, 1911. 



3 Agricultural Journal of Union of South Africa, 1913, vol. 5, p. 915. 



4 Queensland Agricultural Journal, 1914, vol. 2, part I, p. 81. 



s Agricultural Journal of Union of South Africa, 1913, vol. 5, p. 68; 1914, vol. 8, p. 12. 

 6 Rhodesia Agricultural Journal, 1914, vol. 11, p. 579. 



