DISEASES OF THE HORSE. 499 



eastward to the Atlantic and westward to California. It is now a per- 

 manent disease in our large cities, selecting for the continuance of its 

 virulence }' oung or especiall}^ susceptible horses which pass through 

 the large and ill-ventilated and uncleaned stables of dealers and assumes, 

 from time to time, an enzootic form, when from some reason its viru- 

 lence increases. It assumes this form also when, from reasons of rural 

 economy and commerce, large numbers of young and more susceptible 

 animals are exposed to its contagion. 



Etiology. — As one attack is self-protective, numbers of old horses, 

 having had an earlier attack, are not capable of contracting it again; 

 but, aside from this, young horses, especially those about four or five 

 years of age, are much more predisposed to be attacked, while the 

 older ones, even if they have not had the disease, are less liable to it. 

 Again, the former age is that in which the horse is brought from the 

 farm, where it has been free from the risk of exposure, and is sold to 

 pass through the stables of the countr}^ taverns, the dirty, infected 

 railway cars, and the foul stockyards and damp stables of dealers in 

 our large cities. Want of trainmg is a predisposing cause. Overfed, 

 fat, young horses which have just come through the sales stables are 

 much more susceptible to contagion than the same horses are after a 

 few months of steady work. 



Pilger, in 1805, was the first to recognize infection as the direct cause 

 of the disease. Roll and others studied the contagiousness of influenza, 

 and, finding it so much more virulent and permanent in old stables than 

 elsewhere, classed it as a "stall miasm." The atmosphere is the most 

 common carrier of the infection from sick animals to healthy ones, and 

 through it may be carried for a considerable distance. The conta- 

 gion will remain in the straw bedding and droppings of the animal and 

 in the feed in an infected stable for a considerable time, and if these 

 are removed to other localities it may be carried in them. It may be 

 carried in the clothing of those who have been in attendance on horses 

 suffering from the disease. The drinking water in troughs and even 

 running water may hold the virus and be a means of its communication 

 to other animals, even at a distance. The studies of Dieckerhofl', in 

 ISSl, in regard to the contagion of influenza Avere especially interest- 

 ing. He found that during a local enzootic, produced b}' the introduc- 

 tion of horses suffering from influenza into an extensive stable other- 

 wise perfectly healthy, the infection took place in what at first seemed 

 to be a most irregular manner, but which was shown later to be depend- 

 ent on the ventilation and currents of air through the various build 

 ings. His experiments showed that the virus of influenza is exces- 

 sivelj^ diffusible, and that it will spread rapidly to the roof of a building 

 and pass by the apertures of ventilation to others in the neighborhood. 

 The writer has seen cases that have appeared to spread through a brick 

 wall and attack animals on the opposite side before others even in the 



