PARASITES AND PARASITIC DISEASES OF HORSES 49 



and (3) dipping. A fourth method, not in common use but recom- 

 mended by some European investigators, is fumigation with sulphur 

 dioxide. 



HAND APPLICATIONS 



Infested animals may have parasites on any or all parts of the 

 body surface, and to effect complete eradication usually it is neces- 

 sary to cover the entire surface of the skin with the medicament. 

 On account of the difficulty of applying treatment by hand over the 

 entire body surface, hand applications are recommended only as a 

 temporary measure for holding parasites in check until the animals 

 can be dipped or sprayed. 



SPRAYING 



Common parasites on or in the skin can be eradicated by proper 

 spraying, but the method commonly practiced is not economical. 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 projecting 

 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 appa- 

 ratus 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 low for 

 dipping, fumigation is feasible if a large number of horses are to 

 be treated and competent men are available to supervise the work. 

 This method apparently has no other distinct advantage over dipping. 



DIPPING 



Dipping is the most effective known method of applying treatment 

 for common external parasites. Dipping plants are so arranged 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 70 to 80 inches, or sufficient to immerse 

 completely the tallest animal to be dipped. Horses will carry out and 



