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88 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE =| 
ing the eggs or young larve as they hatch, by applying insecticides 
to those portions. One of the most convenient and effective methods 
of accomplishing this is through the utilization of shallow vats. 
In 1918 experiments were begun to determine the effect on the 
infestation of dairy cattle of the use of standard arsenical solution. 
One-half of the cows in a dairy herd was allowed to pass through ~ 
a wading vat containing the solution about 1 foot deep, at invervals 
of four days. The other half of the herd was not treated, being 
kept as a check. In the first year’s test 16 cows were treated and 
the following season these were found to be infested to almost iden- 
tically the same degree as the 16 cows which were not treated. In 
1919 the same herd was utilized in a test under similar conditions, 
a standard sodium arsenite solution containing about 19 per cent 
arsenic trioxide being used in the vat. The following season the 
dipped cows had an average infestation of 7.18 grubs per animal 
and the untreated cows showed an average of 5.65 grubs per animal. 
During the spring of 1920 the same herd was again utilized in the 
same way, except that 18 cows were treated. For charging the 
vat in this experiment a commercial arsenical dip was used which 
in concentrated form was said to contain about 9 per cent of cresol 
salts. In the first two treatments the strength of the solution was 
about 0.19 per cent arsenious oxide. Subsequently this was raised 
to approximately 0.22 per cent. The following spring the treated 
cattle showed an average infestation of 2.5 grubs per head and 
the untreated ones an average infestation of 3.33 grubs each. During 
the spring of 1919 another dairy herd was utilized. Thirteen cows 
representative of the herd in age and breeding were passed through 
a wading vat at 4-day intervals and 14 cows were utilized as a 
control. In this case the vat was charged with a commercial coal- 
tar creosote dip diluted to about 2 per cent. The following season 
a careful check of the grubs in the treated cattle showed an average 
of 6.58 per animal, and the untreated animals showed an average 
of 3.84 grubs each. The following year a similar test was carried 
out at the same dairy. A count of the grubs present in the treated 
and untreated groups made on December 30 showed an average of 
6 per animal in the case of the former group and 8.14 in the latter. 
In a subsequent examination made on February 7, the treated animals 
showed an average infestation of 2.75 grubs each and the untreated 
animals an average of 2.67 each. 
It is possible that better protection would be afforded should the 
dipping be done every day. It would not be feasible, however, to 
dip so frequently with the strengths of solutions used and endeavor 
to cover a greater portion of the legs by having the solution deeper 
in the vats. In the experiments mentioned, the walking of the cows 
through the vats, which were 10 feet long at the bottom and 18 feet 
long at the top, brought the material into contact with the legs con- 
siderably higher up than the actual depth of the dip (1 foot). In 
fact it was found that the udders and bellies of the cattle were fairly 
well drenched, especially on the cows that were inclined to hurry 
through the vat. 
Imes and Schneider (48) have published results of tests with the 
application of used automobile cylinder oil, sodium silicate, and coal- 
tar creosote dip by spraying and wading the cattle through vats 
