332 NASAL CAVITIES. 



Finally, in bronchitis, histological examination leads to the discovery of 

 eggs or embryos of the strongyles. The diagnosis becomes very easy, on 

 post-mortem examination, the identification of the larvae of oestridae being 

 extremely simple. 



Prognosis. The prognosis is only grave when infestation is very 

 pronounced. Most commonly the parasites complete their development 

 without producing disquieting symptoms; as summer approaches they 

 are expelled and recovery occurs. 



Lesions. The only lesions consist in very active inflammation of the 

 mucous membrane of the sinus, which appears excessively hypertrophied, 

 and in the existence of larvae. These develop in the midst of a magma of 

 purulent, foetid discharge. The number of parasites usually ranges from 

 two to twenty, although Ziirn declares that he has found as many as 

 eighty in one subject. 



Treatment. Many precautions have been suggested for preventing 

 infestation. Many are impossible or difficult to carry out in current 

 practice, even the soaking of the nostrils in empyreumatic oil, and the 

 majority are useless. The only suggestion to which we attribute any 

 importance consists in trying to prevent the perfect insects from obtain- 

 ing a lodgment in cavities in the walls or roofs of sheep-sheds. 



The really efficacious modes of treatment are also few in number, for 

 the larvae are so firmly lodged in the mucous membrane of the sinuses that 

 they can only be detached after these have been trephined. The use of 

 nasal injections, embrocations and powders, with the object of making 

 the animal sneeze, are ineffectual. 



Trepanation should not be performed until it is quite clear that the 

 flock is badly infested, and when serious symptoms appear to threaten 

 the lives of some of the animals. 



The operation, although very simple, requires care on account of the 

 thinness of the bones. 



The anatomical directions are the middle line of the head, and a 

 transverse line uniting the upper margin of the two orbits. The orifices 

 are made in the two lower angles produced by the intersection of these 

 lines (Fig*. 169). 



It is then easy to remove with the fingers or forceps the larvae situated 

 immediately below the point of trepanation, and afterwards to wash out 

 thoroughly the cavities of the sinuses. If some lie at points which cannot 

 be directly reached, they can be killed by injecting a little benzine and 

 water. This proceeding is quite safe. 



