Contagious Pneumonia in the Horse. 129 



complicating lesions of the pleura, heart, pericardium, liver, 

 bowels, or kidneys. 



Historic Notes. This affection was formerly confounded with 

 equine influenza, and it was only in the second third of the nine- 

 teenth century that the differentiation was attempted. S. Prange 

 describes this as a special epizootic disease in the French hussars 

 in 1841, L,econturier in Belgium in 18^5, Seidamgrotzky in Ger- 

 many in 1882 (strongly emphasizing the contagion), and Diecker- 

 hoff in Berlin in 1883.. The latter showed that horses, recovered 

 and immune from influenza, still contracted brustseuche and per- 

 ished. This distinction was fully corroborated by lyUstig, Cag- 

 nat (1884), Brun, Delamotte (1886), Jolly, Benjamin, Ivcclainche, 

 Trasbot, and others. The presence of a particulate, living, self- 

 multiplying cause (microbe) was recognized as the essential con- 

 dition of the disease (as we still recognize the necessity for such 

 an organism to explain rabies) though the micro-organism itself 

 was as yet undiscovered. 



At the same time many concurrent factois had to be considered 

 as accessory in different cases. 



Accessory Causes. Young horses often show a greater suscepti- 

 bility than older animals, mainly because they retain all the un- 

 impaired susceptibility of the colt, while old horses have already 

 passed through the disease and become immune. On the other 

 hand, in the absence of acquired immunity, the older, worn out 

 and debilitated animals are the most susceptible and tend to have 

 the disease in its worst form. Susceptibility and immunity are 

 therefore more important factors than mere age. Immunity usually 

 lasts for several years, or throughout life, yet in some animals, 

 or under given conditions, it is overcome much earlier. Inclem- 

 ency of the weather, or special exposure of any kind, as in severe 

 rainstorms, or working with the feet and legs in water, may be- 

 come the occasion of an attack. Exposure to cold north-west 

 storms (America, Atlantic Slope), or north-east (Europe), stand- 

 ing without blanket in a temperature at zero, confinement in 

 draughts of cold air between doors or windows, without clothing 

 and after severe exercise, weaken the whole system and increase 

 susceptibility. The presence of a nasal or bronchial catarrh, or of 

 another debilitating disease may act in the same way. The weak- 

 ened tissues seem to invite the entrance of the germ. Palat, Boi- 



