Purulent Encephalitis. 633 



importance from the clinical point of view, as well as from the patho- 

 logical; since at least in many cases, special methods of treatment may 

 be adopted in eases of the purulent form of the disease. 



(a) Purulent Encephalitis. 



{Cerebral Abscess.) 



Occurrence. The majority of cases occur in young animals 

 and especially in foals, few cases having been recorded in adult 

 horses. Kofler found cerebral abscess in twelve horses out of 

 forty killed on account of staggers. In the otlier species of 

 animals the disease is very rarely observed. 



Etiology. Purulent encephalitis generally results from 

 metastasis in diseases in which pyogenic bacteria are circu- 

 lating in the blood (see page 597). In the horse the majority of 

 cases of cerebral abscess are causally connected with strangles, 

 the vessels of the brain being plugged with emboli composed of 

 infective material. This is supported by the fact that strangles 

 streptococci have repeatedly been demonstrated in the pus. Ac- 

 cording to Dexler strangles is the cause in about 60 per cent of 

 cases. Purulent encephalitis appears to be of very rare occur- 

 rence in other diseases, but it does occur in such conditions as 

 puerperal septicemia (Williams), smallpox (Roll), ulcerative 

 endocarditis, glanders, suppurative pneumonia, pleurisy, and 

 finally pyemia. Trolldenier found a pathogenic streptothrix in 

 cerebral abscesses in a dog (see Vol. I). 



Further causes of cerebral abscess are: injuries to the 

 cranium, and the upper part of the parotid region, suppuration 

 or caries of bones near the brain, and in particular the petrous 

 temporal bone in the dog and the middle ear in the pig and birds, 

 acute inflammation of tlie upper portions of the nasal cavities 

 or the sinuses and the throat, the infective material reaching 

 the brain either along the course of the nerves or the blood ves- 

 sels. Animal parasites may also be responsible for the condi- 

 tion, the larvEB of the CEstrus and Coenurus in the sheep, in cattle 

 larva? of the CEstrus bovis that have wandered into the cranial 

 cavity, larvae of the Gastrophilus in the horse. Finally, the 

 condition may be caused by the penetration of foreign bodies 

 from the pharynx. Durrechoux found a needle in an abscess of 

 the cerebellum in a pig. 



Pathogenesis. When a portion of the brain becomes in- 

 flamed abscess-formation results from the collection of large 

 numbers of pus cells and a softening of the brain tissue. When 

 there is rapid enlargement of the abscess the intracranial pres- 

 sure is increased, white corpuscles escape from the vessels in 

 enormous numbers, and the vessels are dilated. As a result 

 of this, and also owing to the effect of the bacterial toxins on 



