48 INFLUENZA. 



species, and that this diseased condition owes its existence in 

 each species to the reception of its own particular specific 

 poison, and to no other. As so far corroborative of this is the 

 fact, that whatever may be the type of the ej)izootic in any 

 particuhir outbreak, this is in the greater number of the cases 

 maintained throughout the period of its existence in the 

 district. 



.Etiology and Modes of Propagation. 



Generally, in all well-marked outbreaks of influenza, the 

 seizures amongst the horses of a large district of country have 

 beeji so universal, neither age, sex, breed, nor condition 

 either of physical strength or sanitary location apparently 

 influencing its spread, that at a first and casual view causes 

 or determining influences seem to be completely be3^ond our 

 discerning. More carefully considered, however, we find that 

 influenza, like other epizootic, zymotic, and contagious dis- 

 ease, is largely aided in its dissemination over countries and 

 districts, and in its maturation of development in individuals, 

 by predisposing or favouring influences, consisting of, or 

 owing their existence to, certain surrounding conditions 

 which environ the animal, or under which its life and life 

 functions are carried out. 



So largely do these favouring, determining, or j^redisposing 

 influences operate in the distribution and development of 

 influenza, that it is highly probable that the severity of 

 individual cases, as also the rapidity of its dissemination, is 

 more to be attributed to the condition in which the disease 

 finds the jjatient than to any inherent power of the poison 

 itself. 



Although the exact nature of the epizootic influences which 

 give rise to influenza is unknown save in so far as we may 

 be able to observe that, like all other epizootics, it seems, as 

 regards its appearance, virulence, and spread, to be regulated 

 by certain laws, the more potent of these factors or influences 

 which operate in determining or jDredisposing to its appearance 

 are cognizable by every ordinary observer. 



All exhausting and debilitating influences : overwork, bad 

 feeding, unwholesome sanitary conditions — as defective ventila- 

 tion, darkness, dampness, and filth — tend to excessive waste of 

 the component structures of the animal body, as well as pre- 



