PARASITES AND PARASITIC DISEASES OF HORSES 49 
It is difficult to wet the hair coat of an animal with a spray, and 
much of the liquid runs off and is wasted. Spraying is not effective 
unless all parts of the skin and hair are well soaked. 
An ordinary orchard-spraying outfit or a common hand pump 
equipped with hose and spray nozzle may be utilized for spraying 
animals. 
FUMIGATING 
Fumigation consists in exposing animals to the fumes of burning 
sulphur (sulphur dioxide) or some other gas. The animals to be 
fumigated are placed in a gas-tight chamber with the head project- 
ing through an opening and the nose and eyes protected from the 
gas. (Fig. 26.) This method is often recommended for treating 
animals for external parasites. 
Investigations conducted by the Bureau of Animal Industry have 
shown that the present known methods of fumigating animals are 
not suitable for general use. The minimum effective concentration 
of sulphur dioxide for mange apparently is about 4 per cent and for 
lice about 1 per cent. Under ordinary conditions the concentration 
or percentage of gas in the air can not be raised to more than about 
1.5 or 2 per cent by burning sulphur:in the gas chamber unless special 
apparatus is installed. Sulphur dioxide compressed to a liquid and 
stored in steel cylinders is available on the market. By using the 
compressed gas any desired concentration in the chamber within 
certain limits may be obtained. In winter, when the temperature 
is too lew for dipping, fumigation is feasible if a large number of 
horses are to be treated and competent men are available to super- 
vise the work. This method apparently has no other distinct advan- 
tage over dipping. 
DIPPING 
Dipping is the most effective known method of applying treat- 
ment for common external parasites. Dipping plants are so ar- 
ranged that the animals are immersed in hquid deep enough to 
swim in, and the entire body surface is well soaked. For dipping 
horses the dip in the vat should be kept at a depth of 70 to 80 
inches, or suflicient to immerse completely the tallest animal to be 
dipped. Horses will carry out and retain from 2 to 4 quarts of dip 
each, and the depth of the hquid in the vat will be lowered accord- 
ingly. The total estimated quantity of dip which the animals carry 
out plus that required to charge the vat should equal the total quan- 
tity required, provided none is lost by leakage or otherwise wasted. 
The capacity of the vat is usually obtained by multiplying, in 
terms of inches, the average length by the average width, then the 
product by the depth. This gives approximately the number of 
cubic inches of space to be filled with dip. Divide this by 231 (the 
number of cubic inches in a gallon), and the result will be the 
number of gallons of dip needed to charge the vat. (Fig. 33.) 
To obtain the average length, add the length at the bottom to the 
length at the dip line and divide by two. The average width is ob- 
tained in the same manner. The depth should be taken at the center 
of the vat and from the bottom to the dip line only, and not to the 
