INFLUENZA. 59 



poison consists of, and equally difficult to decide whether the 

 morbific principle is generated within the system, or gains 

 access to the system from without. The great nerve 

 centres, the brain and spinal cord, are often affected, the 

 pericardial sac also is frequently affected. The disease 

 is most prevalent in spring and autumn, but in some years 

 it appears in an ej^izootic form. It prevailed to a great 

 extent in Canada in the winters 1867-8. Another great 

 outbreak occurred in 1872, beginning in Toronto. Scarcely 

 a young horse comes into the city without becoming affected 

 by influenza — particularly was this the case during the winter 

 of 1878. The name influenza was applied on account of some 

 influence the stars were supposed to exert over the disease. 

 All animals are liable to its attacks. 



Causes. — Influenza is in all probability primarily and 

 most frequently caused by some atmospheric influence, but 

 is often excited by quartering animals in badly drained and 

 poorly ventilated stables. Animals receiving an insufficient 

 supply of food, in this case also, are more predisposed to 

 the disease. Experience tells us that if an animal is forced 

 to breathe bad air during the greater part of the night and 

 day, he is more susceptible to disease, no matter how 

 well fed he may be, than an animal breathing pure air. 



Contagion. — There may be contagious influences, and I 

 am inclined to think that influenza is a contagious disease 

 under certain circumstances, as, for instance, where large 

 numbers of horses are kept crowded together in large 

 stables — some stables being perfect hotbeds of influenza. A 

 very healthy animal may resist the influence entirely, or at 

 all events for a long period. The disease, so far as I know, 

 has never been produced by inoculation ; it occurs in the 

 most severe form in large cities, and especially in under- 

 ground stables, where, as a matter of course, the ventilation 

 must be imperfect. The coarse breeds of horses are more 



