U. S. DEPARTMENT OF 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. 
