512 DISEASES OF THE HORSE. 



free from the disease, it certainly appears after the introduction of 

 an apparently healthy animal. 



As one attack is usually self-protective, numbers of old horses, 

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

 but, aside from this, yoimg 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 country taverns, the dirty, infected 

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

 our large cities. Overfed, fat, young horses w^hich 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 con- 

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

 influenza were especially interesting. He found that during a local 

 enzootic, produced b}'^ the introduction of infected horses 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 ventilation and currents of air 

 through the various buildings. His experiments 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 ventila- 

 tion 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 same stable were 

 affected. Brick walls, old woodwork, and the dirt which is too fre- 

 quently left about the feed boxes of a horse stall will hold the con- 

 tagion for several days, if not weeks, and communicate it to sus- 

 ceptible animals when placed in the same locality. On two succes- 

 sive mornings a 4-year-old colt belonging to the writer stood for 

 about 10 minutes at the open door, fully 40 feet from the stalls, of a 



