INFECTIOUS DISEASES. 5738 
mitted to cattle, buffaloes, sheep, goats, rabbits, guinea pigs, rats, 
and monkeys. No birds, reptiles, amphibia (frogs, etc.), or fish are 
known to suffer from it. It attacks both male and female animals, 
young and old. Australian breeds of horses and white and gray 
mules are said to be more susceptible than animals of other breeds 
and color. 
Surra in equines and camels is said to be an invariably fatal dis- 
ease, but cattle occasionally recover from it. There is no history of 
a definite onset of the disease, and the condition is progressive, 
usually with a number of relapses. The period of incubation may 
vary somewhat; in experimental cases it is from 2 to 75.. (usually 
6 to 8) days, according to conditions. The duration varies with 
the species of animal attacked, their age, and general condition. The 
average duration in the horse is reported at less than two months, 
though some cases may terminate fatally in less than one to two 
weeks. ' m3 
Method of infection.—All evidence now available seems to indi- 
cate that surra is strictly a wound disease, namely, that the parasite 
may enter the body only through a wound of some kind. Appar- 
ently by far the most common method is through wounds produced 
by biting flies whose mouth parts are moist with the infected blood 
of some animal bitten by the same flies immediately before biting 
the healthy animal. Crows may also transmit the infection by peck- 
ing at sores on a diseased animal, soiling their beaks with blood, 
and transferring. this infected blood to a healthy animal. Likewise, 
if a scratch is made on a horse and then infected blood is rubbed 
on the scratch, the horse will become diseased. If, in experiment, 
infected blood is fed to a healthy animal, the latter may contract 
surra in case it has an abraded or wounded spot in the mouth; but 
if no part of the lining of the alimentary canal is wounded, infec- 
tion does not take place. Thus dogs and cats may contract the dis- 
ease by wounding the lining of the mouth (as with splinters of bone) 
while feeding on the carcasses of surra subjects. All available 
evidence indicates that under normal conditions of pregnancy the 
disease is not transmitted from mother to fetus. 
There is a popular view that’surra may be contracted by drinking 
stagnant water and by eating grass and other vegetation grown upon 
land subject to inundation, but there is no good experimental evi- 
dence to support this view. Probably the correct interpretation of 
the facts cited in support of this theory is that biting flies are numer- 
ous around stagnant water and in inundated pastures; hence, that 
a great number of possible transmitters of the disease are present 
in these places. aS 
