88 DISEASES OF 



frequently see it in aged horses. Horses kept in small 

 and badly ventilated stables are more liable to the dis- 

 ease than those kept in large, well ventilated stables. 

 Horses that are hard worked, especially while young, 

 will suffer more severely than those that are kept in a 

 strong, hardy condition. Change of food will also act 

 as a cause, as when horses are shipped from the farm 

 where they are fed on some kind of soft food to large 

 cities, where they are immediately placed on a diet of 

 dry food and usually in much larger quantity than they 

 received while in the country. Undue exposure to in- 

 clement weather is frequently a cause. It will be no- 

 ticed that the various causes above enumerated all act 

 by depressing the vitality of the horse, thus making 

 him an easy prey to disease. 



It is now perfectly well understood that all contagious 

 diseases are caused by some living organism gaining 

 access to the interior of the body, and there setting up 

 a destructive action of some kind. Influenza in horses 

 is no exception to this rule, although the particular 

 germ which causes it has not been isolated and experi- 

 mented with to the extent that it can be easily identified. 

 Several observers have described germs which they 

 assert to be the cause of influenza in horses, but as yet 

 there is no particular germ accepted by all experiment- 

 ers as the cause of this disease. The germs, however, 

 are certainly the active cause of all forms of distemper. 



How do the germs cause the disease ? Most likely 

 they act in several wa} r s, each setting up a special form 

 of the disease. We will first describe the most common 

 form, where we have about the following: 



Symptoms. The animal is first noticed to lag more 

 than usual at work ; then a loss of appetite, or, if a mild 



