446 INFLUENZA IN HORSES 
of 10 per cent. It is stated that in 1872, in Philadelphia, 7 per cent. of 
30,000 infected horses died. 
Morbid anatomy. The principal tissue change is the acute 
hyperemia of the mucous membrane of the digestive tract which may 
also be swollen and sprinkled with slight hemorrhages. The sub- 
mucosa is yellowish in color and infiltrated with a gelatinous substance 
causing the membrane to form thick, somewhat translucent, eleva- 
tions containing a fluid which coagulates. Peyer’s patches are 
enlarged, especially those in the neighborhood of the ileo-cecal valve. 
The mucous membrane of the mouth and sometimes that of the 
pharnyx show similar changes. 
The mucous membranes of the upper air passages are hyperemic 
and swollen. In rare cases, the mucosa of the larynx is inflamed, also 
the subcutis when inflammatory swellings appear on the skin. Schutz 
found that in the brain and spinal cord the arachnoid spaces are filled 
with a fluid which is generally clear, although it may contain leuco- 
cytes. He reports one case in which the lateral ventricles contained 
a large quantity (20 c.c.) of fluid. The other lesions which may be 
found depend upon the extent or localization of the disease. Usually 
the spleen is slightly enlarged; small hemorrhages in the intestines, 
under the serous membranes and in the lungs, eyes and brain; gela- 
tinous infiltration of the renal connective tissue and mesentery; 
swelling of the lymph glands; yellowish serous exudates in the larger 
cavities of the body and imperfect coagulation of the blood. One or 
all of these changes may appear in a single animal. There sometimes 
occur edematous swellings of the subcutaneous tissue on various parts 
of the body. 
Diagnosis. Influenza is diagnosed by the symptoms and its infec- 
tious nature. A rise in temperature is an important diagnostic 
feature in times of an epizodtic. There is no specific test. It is to 
be differentiated from strangles, contagious pleuro-pneumonia, 
petechial fever and catarrhal conditions of the head. 
Prevention. The removal of uninfected horses from infected 
stables is important. Newly purchased horses should be kept 
separate from the others for some days unless their source and non- 
exposure in sale stables and cars are known. Many efforts to immu- 
nize horses with vaccines have been made and also with the blood 
of recovered animals but uniform satisfactory results have not been 
obtained. 
