PAEASITES 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 

 connpressed gas any desired concentration in the chamber within 

 certain limits may be obtained. In winter, when the temperature 

 is too low 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 liquid 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 TO to 80 

 inches, or sufficient 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 liquid 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 



