INFLUENZA IN HORSES 443 
laid stress on its contagious nature and stated that in his opinion ‘“‘a 
volatile infectious matter was the cause.” 
Influenza spread as an epizootic in 1872 to 1873 over the greater 
part of the United States where it received the name of “pink eye” 
(French, fiévre typhoide). It started in Canada and extended south 
and west, reaching into British Columbia to the north and Mexico at 
the south. The last great epizodtic raged in Europe from 1881 to 
1883 during which time it is said to have spread over nearly the whole 
continent. In the Prussian army, 3,434 horses became affected in 
1890; 2,497 in 1891; and 3,645 in 1892. In Copenhagen, 3,000 
horses were affected in 1890 and 1891. 
Geographical distribution. Influenza seems to be known in nearly 
if not all of the countries of Europe and America. In certain sections 
of the United States it is an almost constant affection. This is espec- 
ially true of certain cities, owing to the constant introduction of 
“‘green’’ horses. 
Etiology. Influenza seems to be produced by a specific infection 
the nature of which has not yet been determined. A number of 
bacteria have been described as the probable cause but thus far none 
of them have been found to be sufficiently constant to warrant their 
acceptance as the etiological factor. Ferry has recently emphasized 
the presence of streptococci in the tracheal mucus and in the blood. 
The infecting agent spreads rapidly among horses. The virus appears 
to lose its virulence quickly outside of the animal body, but within 
the body it seems to be preserved for a long time. According to the 
observation of Jensen and Clark, stallions which have had the disease 
may transmit it to the mares they serve for months after apparent 
recovery. Some believe the cause to be a filterable virus. Diecker- 
hoff succeeded in transmitting the disease to healthy animals by sub- 
cutaneous and intravenous injections of the blood of infected horses, 
but Friedberger and Arloing failed to do so. Horses are most sus- 
ceptible. Sex, breed, stable management and feeding appear to have 
little or no influence on their individual susceptibility. 
Infection usually takes place from horse to horse. through the secre- 
tions and excrements which are especially infectious during the devel- 
opment and at the height of the disease. Convalescent animals often 
eliminate the virus. The general belief is that the horse becomes 
infected through the digestive tract. It is not disproven that infec- 
tion may occur through the respiratory organs. The virus appears 
