Etiology. 597 



Etiology. Simple meningitis (primary or idiopathic men- 

 ingitis) is with few exceptions cine to an infection, the infective 

 material reaching the brain by way of the blood stream. The 

 causes of the disease are only imperfectly known. 



In the horse primary meningitis is not rarely a sporadic 

 case of enzootic cerebro-spinal meningitis and is set up by the 

 cause of that disease. This view receives strong support from 

 the more recent investigations of Christiani. This author found 

 diplococci agreeing with the cause of Borna disease on the one 

 hand and with the micrococcus of cerebro-spinal meningitis of 

 Weichselbamn in all its characters on the other, in the spinal 

 fluid of practically all his cases of socalled acute hydrocephalus 

 in the horse. The diplococci were never found in horses suffer- 

 ing from other diseases of the brain. 



There is no room for doul)t that for certain cases of pure 

 meningitis in the horse and in otlier animals other infective 

 materials are responsible. On the otlier hand, observations made 

 on the human subject show that organisms present in the healthy 

 body may play some part in the production of the disease, either 

 owing to some exaltation of virulence, or owing to some de- 

 crease of resistance on the part of the body. Streit found the 

 bacillus necrophorus in meningeal exudates of two horses. 



According to Poulsen sporadic cases of simple meningitis 

 occur in cattle at all periods of the year. Cases are more fre- 

 quent in young animals than in adults and the cause is not ex- 

 actly known. Poulsen further observed cases following calv- 

 ing which were apparently due to this, but quite distinct from 

 parturient paralysis. This disease he named puerperal menin- 

 gitis. The disease developed without exception one or two days 

 after calving, never later, and never before calving. Christiani 

 found diplococci comparable to the streptococcus of Borna dis- 

 ease in a goat affected with acute meningitis. 



Miscli found cocci in two cases of meningo-encephalitis in 

 the rabbit, cultures of which set up a similar disease by in- 

 travenous inoculation into experimental animals. 



According to Klee a special form of acute meningitis occurs 

 in the pigeon (the socalled staggers [see disease of the vestibular 

 nerve] ) caused by a bacterium measuring 1 to li/4 i*- in length. 



There are certain exciting causes that play some part in the 

 production of simple meningitis. Among these may be men- 

 tioned: bad weather (cold and wet), chills, concussion of the 

 brain, long exposure to the sun, transport by train, intensive 

 feeding, overexertion, etc. Up to the present no exact observa- 

 tions have been made to ascertain to what extent the direct rays 

 of the sun may be responsible for meningitis. Cases are prin- 

 cipally observed in young animals and in geldings that are 

 housed in hot, damp stables, and fed on a rich diet ; circum- 

 stances which predispose to infectious disorders. Christiani, 

 on the other hand, was unable to show that even a long period 

 in a stable that was damp had any predisposing effect. It is a 



