328 PRINCIPLES OF VETERINARY SCIENCE 



mercury so is very poisonous and cannot be used with safety 

 except on poultry. Kerosene emulsion or kerosene with equal 

 parts of cottonseed oil is an effective remedy when applied 

 thoroughly and repeatedly. Foremost among the liquid in- 

 secticides are the various commercial coal-tar dips. The latter 

 should be used in accordance with the directions of the manufac- 

 turer as printed on the label accompanying the original package. 

 Spraying is the method used when the number of animals 

 to be treated is too large to justify making hand applications, 

 or too small to justify providing a dipping vat. Any liquid 

 insecticide mentioned above may be applied as a spray. Two or 

 more treatments should be given fifteen to sixteen days apart. 



Fig. 82. — The bot-fly of horse (Gastrophilus equi). An adult female magnified 

 about three diameters. 



Dipping consists in immersing animals in a vat containing a 

 liquid that will kill external parasites. To be successful, dipping 

 must be performed carefully and thoroughly. Full directions 

 for dipping cattle to eradicate lice may be found in Farmers' 

 Bulletin 909 issued by the United States Department of 

 Agriculture. 



The horse bot is the larva of the bot-fly (Gastrophilus equi) 

 (Figs. 82 and 83). The female is woolly abd gray brown in 

 color. It hovers around the legs and neck, where, it deposits 

 eggs and cements them with a special secretion to the hair. 

 These flies are most active in the hot summer months. After a 

 time the eggs hatch and the minute larva irritate the skin, 

 causing the host to bite the infested part. In this way they gain 



Digitized by Microsoft® 



