SIMPLK PNEUMONIA IN THE HORSE. 1 73; 



a common disease in the horse. Its frequency is explained, especially 

 in horses used for heavy work in large towns, by the changes of tem- 

 perature to which they are exposed, by the very active function of the 

 lung during work, and by the susceptibility to cold presented by those 

 kept in ill-ventilated stables. 



Liability to pneumonia varies with age. The disease is commonest 

 in young unseasoned animals, which are particularly sensitive to the 

 action of changes in the weather, and in which the lung has not yet 

 become accustomed to active work. In them, and in old animals which 

 have arrived at the decadent period, the disease is gravest. Among 

 predisposing influences are close, low-roofed, badly ventilated stables ; 

 debility ; sluggish circulation ; and various other causes which 

 commonly favour the development of visceral diseases. 



The chief exciting cause of pneumonia is the action of cold. In 

 this respect authors are unanimous, and in consequence the disease has 

 often been termed Pneumonia a frigorc. The largest number of cases, 

 occur during the first four and last three months of the year. It is par- 

 ticularly frequent at the seasons of greatest changes in temperature — at 

 the beginning of spring, and in the autumn. Sudden changes of tempera- 

 ture, and rain or moist weather, appear more dangerous than prolonged 

 uniform cold. Chills, thus produced, may be assisted by other influences, 

 especially by functional hyper-activity of the lung. The most fa^■ourable 

 conditions for producing pneumonia are found when animals have been 

 clipped, and whilst sw^eating are wetted b}- a shower, or suddenly 

 exposed to a current of cold air. It is said that since the custom of 

 clipping has become general, pneumonia has diminished in frequence. 

 Nevertheless cases occur where it clearly appears to have favoured 

 inflammation of the lung. In one of our patients, which had not been 

 overworked or exposed to showers, pneumonia developed ten days after 

 clipping. Many similar cases have been observed amongst the horses 

 of the great Omnibus Company of Paris, where clipping has been 

 given up. 



For a long time it was belie\ed that the action of cold was alone 

 sufficient to produce pneumonia, but this is erroneous. The constant 

 failures which followed attempts to produce pneumonia experimentally 

 were explained by a special resistance of the organism, and by the 

 absence of conditions which predispose to the disease. Bacteriological 

 experiments in man have, however, shown the existence of another 

 factor, which is, in fact, the causa causans. They proved that pneu- 

 monia is an infectious disease, produced by the entrance into and 

 growth within the lung of a special microbe — the pneumococcus. 



The first experiments on this point date from 1877. Some years. 



