MANAGEMENT OF THE WEANLINGS 
105 
attached to the droplets, and later enter the upper air passages of healthy 
animals. This form of transmission through the air is less dominant out 
of doors, first on account of the smaller quantity of moisture, and second 
on account of its more rapid movement, which results in the rapid dilu¬ 
tion of the expelled virus. 
“Through contamination with nasal discharge and pus from the glands 
the most varied objects may become carriers of the infection, such as 
cribs, drinking utensils, the food, the drinking water, straw, walls, floor 
of the stables, the grass in the pasture, further the hands and clothes 
of the attendants. The fresher the secretion the greater its virulence; 
drying, however, does not wholly destroy its infectiousness. The disease 
usually occurs annually almost at the same time of the year in stables of 
colts, if they have not in the meantime been cleansed and disinfected. It 
usually appears in the spring, and it is not possible in all instances to 
prove a fresh introduction from the outside. In such cases it must be 
assumed that the virus remained in the stable after the disappearance 
of the disease, and was there dormant for months until it again attacked 
the susceptible individuals of the new generation of colts, and thereby 
caused a new outbreak of the disease. 
“The infection probably enters from the digestive tract and especially 
through the intestinal mucous membranes in those cases in which it 
affects primarily or exclusively, the lymph glands of the mesentery. 
However, up to the present time it has not been possible to produce this 
form of the disease by feeding infected food. 
“In copulation an infected stallion may transmit the disease to mares, 
and in such cases there appear symptoms of a vaginal catarrh, while the 
lymph glands in the vicinity of the external genital organs and of the 
rectum, as well as in exceptional cases also the udder, become affected 
. . . Affected colts may infect their mothers during sucking and cause 
an inflammation of the udder and the neighboring lymph vessels . . . 
“There is another possibility . . . that . . . the streptococci of 
strangles may live outside of the animal bodies as saprophytes, and under 
favorable conditions may attack colts, especially when the animals are 
weakened by outside influences. In this manner those cases can be ex¬ 
plained in which the disease appears in localities after years of absence, 
without any demonstrable introduction. 
“Solipeds are exclusively susceptible to the disease, and they become 
infected at the age of one-half to 5 years, mostly, however, while they are 
colts. In rare cases the disease may occur at the age of 1 to 2 months 
and also in animals over 5 years of age. The greater susceptibility of 
young animals is associated with the lesser resistance of their mucous 
membranes. The greater resistance of older animals is, however, prob¬ 
ably the result of their having already passed through an attack of the 
disease ... it usually attacks animals only once during their lives 
. . . some horses may become affected repeatedly, but in such cases 
the attacks are usually separated by intervals of several years, while 
cases in which an animal becomes repeatedly infected in one year . . . 
are exceptionally rare. 
“Outside influences which reduce the natural resistance of the animals, 
especially colds, favor the infection, by causing a catarrh of the mucous 
membrane of the air passages, as a result of which the epithelia become 
loosened, and thereby the bacteria colonize more readily in the profusely 
accumulated secretion, from which they may penetrate the tissue of the 
mucous membrane. 
“Usually weakened and poorly nourished colts are particularly sus¬ 
ceptible to the disease. In this regard, stabling in poorly ventilated, ex¬ 
cessively warm stables, insufficient feeding, sudden changes of weather, 
fatigue during transportation, also pre-existing illness have a modifying 
effect on the individual susceptibility. The cases in older horses usually 
