DISSEMINATION AND CONTROL OF TEXAS FEVER. 
401 
at this; he knows that the same is true with all communicable dis¬ 
eases, and that it is precisely where these are most common that 
there is the greatest doubt as to the manner of their origin and 
dissemination. Every unbiased man is ready to admit, for in¬ 
stance, that pleuro pneumonia never occurs in this country unless 
it is contracted from a previously sick animal, because the disease 
was never known here before it was imported from Europe, and 
because it never occurs now beyond the area obviously infected, ex¬ 
cept by contagion. And yet, when we consult the people of the in¬ 
fected districts, we find that many are emphatic in their assertions 
that the disease occurs spontaneously as the result of certain con¬ 
ditions of the atmosphere or food, and that it does not arise in 
all cases from contagion. The reason is very plain. The conta¬ 
gion is so generally disseminated that it is impossible to trace a 
large number of the cases to their origin, and they are, conse¬ 
quently, accepted as spontaneous. If we go to France, we find a 
still more general acceptance of the opinion that this disease 
arises spontaneously, and this is even shared by many members of 
the veterinary profession. But as the disease is becoming more 
circumscribed, and as greater efforts are being made to trace the 
origin of the outbreaks, the profession, at least, is gradually be¬ 
coming convinced that it only arises by contagion from pre-exist¬ 
ing cases. 
Along the border line for miles beyond the district perma¬ 
nently infected with Texas fever, every road and common is in¬ 
fected in early spring by the continuous movement of cattle, and 
it is not surprising that many outbreaks of the disease can never 
be traced to their source. So, too, in many cases where South¬ 
ern cattle are carried farther North, an unsuspected road or com¬ 
mon is infected, and it long remains an unsolved mystery how 
the native cattle contracted the disease. Again, people fre¬ 
quently forget that foreign cattle were on their roads and pas¬ 
tures, it may be, three to five months before the outbreak of the 
disease ; they are almost as likely to forget that their own cattle 
have been on certain roads or pastures within three to six weeks ; 
they even forget that they have purchased cattle lately enough to 
cause the infection, and in all these case^ they will assert most 
