2 BULLETIN 76, U. S. DEPARTMENT OE AGRICULTURE. 



receives a setback, not only through the wasted labor of ineffective 

 dippings or the economic loss of injured cattle, but still more through 

 the arousing of distrust or even enmity in those very persons whose 

 willing cooperation in tick -eradication work is most to be desired. 



The causes which may lead to the use of a bath of the wrong 

 strength are rather numerous. Impure materials may be purchased; 

 mistakes in measurements or computations are sometimes made even 

 by a careful man. But these things can all be checked and guarded 

 against; the greatest difficulties arise in maintaining the bath at the 

 right strength, once it has been prepared. A fresh bath can not be 

 made up every time a few cattle are to be dipped. Practical con- 

 siderations render it necessary to use the bath over and over again, 

 perhaps during a period of several months, sufficient fresh fluid 

 being added from time to time to replace that carried out by the 

 cattle. During such a period of time, especially in the hot summer 

 weather, evaporation of water from the dip naturally tends to con- 

 centrate it. This may be compensated for in a measure by marking 

 the level of the dip on the side of the vat before a period of disuse, 

 and then filling up to the mark with water when the dip is used 

 again. But it is difficult to construct a vat holding one to three 

 thousand gallons so as to be entirely free from leaks. Therefore it is 

 uncertain in any case how much of the lowering of the level of the 

 dip is attributable to evaporation and how much to leakage. Leakage 

 may likewise be in as well as out; that is, rain, surface water, or 

 ground water may enter the vat. 



Even if these difficulties are avoided, there is still another factor 

 which evades all precautions, the fact that used arsenical dipping 

 fluids may in course of time undergo a process of oxidation whereby 

 the arsenious oxid originally present as sodium arsenite is converted 

 to arsenic acid or sodium arsenate. Various observers have noted 

 such a tendency, but have usually attached little importance thereto, 

 assuming it to be caused by a slow and relatively insignificant 

 chemical reaction. It has remained for Fuller, 1 working in this 

 laboratory, to show that the change is essentially caused by the 

 growth of microorganisms in the fluid— that is, it is a biological 

 process and not a simple chemical action — and furthermore that it 

 may become very extensive, converting nearly all the arsenic into 

 the oxidized form. Tests by the Zoological Division of the bureau 

 indicate that arsenic in the form of arsenate is probably a less effective 

 tickicide than when present as arsenite, while at the same time 

 decidedly poisonous to animals. Laws, 2 as the result of a certain 

 number of experiments, has concluded that arsenic, existing as arse- 



1 Bureau Animal Industry Circular 182. 



2 Laws. The Tick-killing Properties of Sodium Arsenate. The Agricultural Journal of the Union of 

 South Africa, 1913, vol. 5, p. 915. 



