.ETIOLOGY AND MODES OF PROPAGATION. 51 



indirect means, can be discovered. Or its appearance may 

 even have been suddenly more extensive ; it may, instead of 

 attacking one or two animals in a particular stud, have made 

 a simultaneous invasion of several studs over a considerable 

 extent of country. Knowing, however, the great difficulty 

 there often is in tracing from their source of origin to a fresh 

 and new field of development even undoubted and incontro- 

 vertibly contagious diseases, as in the case of epizootic pleuro- 

 pneumonia and rinderpest, we are disposed to consider of 

 greater value a few well-authenticated cases of orio-in from 

 direct contact of diseased with previously healthy animals, 

 than many recorded instances of attacks or invasions, where 

 the most that can be said is that, as far as we know, contagion 

 has had no share in the appearance and development of the 

 disease. 



That influenza may not be propagated by inoculation re- 

 quires further proof, while what has already been done in this 

 direction is susceptible of a different interpretation. From my 

 own experience of this disease, an experience pretty extensive 

 and particularly bearing upon the question of its propagation, 

 I am disposed to regard it as contagious, and capable of trans- 

 mission from the actually suffering to the healthy animal. 



There undoubtedly does appear to be a difference as to its 

 powers of propagation in different phases or developments of 

 the disease, the mildest and most benign manifestations evi- 

 dently possessing this power in a much less degree than those 

 more decided and malignant types of the fever. 



I have for many years had opportunities of observing that 

 the occurrence of influenza amongst agricultural horses, when 

 the disease existed — for it is not every season that this fever 

 is met with in an epizootic form — has borne a direct relation 

 to the numbers of imported animals, i.e. animals brought by 

 dealers from a distance into the district of which I speak — the 

 border counties of England and Scotland, 



Now this is exactly what was experienced in the same 

 district in the case of epizootic pleuro-pneumonia in cattle, 

 when that disease was infinitely more common than it is now. 

 Being in reality a feeding, not a breeding, district, there was 

 the periodical necessity for an importation of fresh stock ; and 

 as surely as this fresh supply entered the district, so surely 



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