174 CLINICAL VETERINARY MEDICINE AND SURGERY. 



later Friedlander discovered in centres of pulmonary inflammation an 

 encapsuled bacillus, which he regarded as the cause of the disease. 

 Talamon afterwards found that the microbe of the disease is a coccus 

 occurring in the form of little elongated grains, isolated or arranged in 

 couples, and enclosed in a capsule ; it colours readily with aniline dyes 

 and by Gram's method. This pneumococcus had previously been dis- 

 covered by Pasteur in normal saliva. It exists in the bucco-pharyngeal 

 cavity, and has also been found in the nasal fossae, Eustachian tubes, 

 and even in the bronchi. Nor is its field of pathological activity limited 

 to the lung. It may produce pleurisy. It is also capable of passing 

 into the blood-stream and causing other visceral diseases like endo- 

 carditis, nephritis, and meningitis — only to mention the principal. 

 Cultures of this pneumococcus injected into the blood produce pneu- 

 monia, sometimes complicated with pleurisy, endocarditis, and peri- 

 carditis. 



In human pneumonia it is constantly present, and without it the 

 disease does not develop. Invasion of the lung is favoured by cold, 

 which, however, only acts as an exciting cause by producing vascular 

 or cellular disturbance, and by momentarily diminishing the resistance 

 of the organism. The pneumococcus does not always act alone, being 

 sometimes accompanied by streptococci or staphylococci. Even when 

 the pathogenic organisms are confined to the lung grave disturbance 

 may be produced in other viscera or tissues by the toxins they 

 elaborate — that is, by soluble poisons, the injurious effects of which 

 are specially marked in the heart and kidneys. 



Simple pneumonia in the horse is certainly an infectious disease 

 also, but its microbe has not yet been satisfactorily identified. In 

 hepatised areas various germs are found, among others a micrococcus 

 which presents certain analogies with the pneumococcus of man, and 

 a diplo-streptococcus which, according to certain authors, is only a 

 modified form of the microbe of contagious pneumonia. 



It is possible that, as in man, the microbe which produces simple 

 pneumonia acquires greater virulence by growth in the favourable 

 medium offered by the inflamed pulmonary tissue, and that, having 

 gained this increased activity, it may unaided produce pneumonia in 

 animals exposed to infection. Such infection might easily occur 

 through the medium of the discharge, which always contains a certain 

 number of the infective organisms. 



Against this theory of the contagious character of simple pneu- 

 monia, suggested by Cagnat in 1884, have been advanced innumerable 

 recorded cases where the disease remains isolated, and where, in spite 



