PREVENTIVE MEDICINE 347 



the ground, this is working for the pests and not against them. 

 Warbles persist owing to carelessness and indifference. If shelter 

 sheds are provided in the fields cattle will take cover in them when 

 pursued by the flies which will not enter a shed. The injection of 

 one drop of tincture of iodine into the tumour kills larvae. Lucet 

 recommends the simpler method of stabbing the grub with a heated 

 lancet or knitting needle. Glaser found that birch oil, which 

 is very cheap, applied to the hides of cattle before leaving the 

 sheds for the pastures effectively kept the flies away.* 



Lard, cart grease, vaseline, or other fatty or oleaginous sub- 

 stance, applied fairly thickly over the nodules, blocks up the 

 " breathing hole " in the skin and suffocates the larva. 



THE SHEEP NOSTRIL FLY. 



The sheep nostril fly, Ostrus ovis, belongs to the same family 

 as the warble flies, the Oestrida;, and like them has only rudimentary 

 mouth parts and is unable to feed in the adult state, consequently 

 its life, as a fly, is short. The female lays either eggs, or larvae 

 already hatched, about the nostrils of sheep in the months of July 

 and August. If the weather is unpropitious the female does not 

 fly abroad, but waits for a fine day; it is under these conditions 

 that the eggs hatch out within her body and larvae are then extruded 

 in the place of eggs. The larvae crawl up the nostrils and attach 

 themselves to the mucous membrane in the nostrils or in the air 

 sinuses. There they remain feeding for about ten months and 

 drop out from March to May. When nearly ready to leave the 

 air passages for their pupation period they crawl down the nostrils 

 thereby irritating its sensitive lining membrane and causing the 

 sheep to sneeze, which act hastens their expulsion. They pupate 

 just beneath the soil. Though the actual mortality from these 

 maggots is negligible, sheep badly infested lose flesh and depreciate 

 in value. 



PREVENTIVE MEASURES. Prevention may be effected by smear- 

 ing the noses of the sheep with tarry dressings that repel flies seek- 

 ing to alight. Fillers suggests the use of salt-boxes so designed 

 that the sheep smear their noses with oil and tar when they use 

 the box.f Another effectual method which is in common practice 

 is to draw a single furrow across every 40 or 50 yards of the field 

 in which the sheep are herded in the hot season. During the heat 



* Second Report of the International Commission for the Preservation, 



Cure and Disinfection of Hides and Skins. 

 1 System of Vet. Med., Wallis-Hoare, 1915, Vol. II., p. 1431. 



