492 



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 cajjable 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 contamination, and is 

 sold to pass through the stables of the country taverns, the dirty, 

 infected railway cars, and the foul stockyards and damp dealers' sta- 

 bles of our large cities. Want of training is a predisposing cause. 

 Overfed, fat, young horses, which have just come through the sales 

 stables, are much more suscex:)tible to contagion than the same horses 

 are after a few months of steady work. 



Pilger, in 1805, w^as 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 atmos- 

 phere is the most common carrier of the infection from sick animals 

 to healthy ones, and through it it may be carried for a considerable 

 distance. The contagion will remain in the straw bedding and drop- 

 pings of the animar, and in the feed in an infected stable, for a con- 

 siderable time, and if these are removed to other localities it may be 

 carried in them. It maybe carried in the clothing of those who have 

 been in attendance on horses suffering from the disease. The drink- 

 ing 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 Dieckerhoff, in 1881, in regard to the contagion of 

 influenza were especially interesting. He found that during a local 

 enzootic, produced by the introduction of horses suffering from 

 influenza into an extensive stable otherwise perfectly healthy, the 

 infection took place in what at first seemed to be a most irregular 

 manner, but which was shown later to be dependent on the ventila- 

 tion and currents of air through the various buildings. His experi- 

 ments showed that the virus of influenza is excessively 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 spread through a brick wall and attack animals on the 

 opposite side before others even in the same stable were affected. 

 Brick walls, old woodwork, and the dirt which is too frequently left 

 about the feed boxes of a horse stall, will all hold the contagion for 

 some days, if not weeks, and communicate it to susceptible animals 

 when placed in the same locality. A four-year-old colt, belonging to 

 the writer, stood at the open door of a stable where two cases of influ- 

 enza had developed the day before, fully 40 feet from the stall, for 



