]^76 Influenza of Horses. 



elements of affected horses, contaminated food, straw, manure, 

 stable utensils, cribs, pails ; people who are employed in hand- 

 ling sick animals, their clothing, etc. The virus may retain its 

 virulence for a long time in poorly ventilated, musty and damp 

 stables, while in pure, dry air and under the influence of sun- 

 light it loses its virulence within a short time. These condi- 

 tions may explain the fact that outbreaks usually remain con- 

 fined to individual stables or townships, or to limited localities, 

 and that a wide extension of the disease, such as is the case, 

 for instance, in foot-and-mouth disease, is rarely observed. 



The possibility of the infection being transmitted by flies, as intermediate 

 carriers of the virus (Giesecke), is not at all probable in consideration of the mode 

 of appearance and extension of the disease, and especially in view of the frequent 

 localization of the affection in individual stables. 



The infective agent, as a rule, enters the animal body 

 with the feed or drinking water, and very probably through 

 the intestines or through the lymphatic pharyngeal ring 

 (Walther) ; however the possibility of infection through the 

 air passages should not at the present time be disregarded. 



Pecus reports on observations of outbreaks in which the infection could only 

 have occurred through the digestive tract; in several stables only those horses became 

 affected which drank from a common trough, whereas the horses which were watered 

 with individual pails escaped the disease. One particular horse drank from a pail 

 the contents of which was contaminated by the discharge of an animal affected with 

 influenza, and this horse developed the disease in six days. 



Of the predisposing causes of the disease colds should 

 come first in consideration. Experience also points to this 

 fact, that the beginning, and the greatest extension of the dis- 

 ease, is frequently associated with northern or eastern winds, 

 and the frequent occurrence of the disease in the cold, damp 

 periods of the year can be traced to this. Catarrhal affection 

 of the mucous membranes is another predisposing cause for 

 the disease, and owing to this fact the mortality. among horses 

 which are kept in badly ventilated stables is usually greater 

 than under more favorable hygienic conditions. 



The age of the animals has an influence on their suscep- 

 tibility, inasmuch as horses over one year of age are most 

 readily affected with the disease, while it occurs less frequently 

 among very old animals. The disease occurs with greater 

 frequency and in a more severe form among horses of high 

 breeding, as well as among the heavier breeds. All solipeds 

 are susceptible to the disease. 



One attack of the disease diminishes the susceptibility to 

 infection for only a short time. We have observed horses at- 

 tached to the medical (army) service which passed almost every 

 year through a slight attack of influenzal pneumonia. 



Pathogenesis. As the primary cause of the disease is at 

 present unknown, only suppositions are admissible relative to 

 its method of action. The infective agent produces a general 

 blood infection which is manifested in general febrile and 



