IMMUNITY AND PROTECTIVE INOCULATION 513 
they would produce cannot appear, and if the individuals already 
suffering from the disease are properly isolated, their stables and pens 
disinfected, and their bodies properly destroyed if they die, the infect- 
ing organisms must perish. Pasteur said, “It is within the power of 
man to make all infectious diseases disappear from the world.” The 
fact that the microdrganisms of these diseases are parasites restricts 
their breeding places, so to speak, to the animal body. If, therefore, 
the channels through which these microdrganisms escape from the 
infected body are properly guarded, and if the channels through which 
they enter the healthy body are intelligently protected, the spread of 
infectious animal diseases will be minimized, if not entirely prevented. 
Since the discovery of a specific etiology the life history and possi- 
bilities of the virus of the different infectious diseases have been 
diligently studied and much has been learned concerning them. The 
result is that frequently by taking advantage of the present knowledge 
of the infecting organism, preventive measures may be taken that 
will give equally as good results as vaccine, without its dangers, and 
often with as little trouble and expense. The prevention of these 
diseases is well illustrated in many instances where owners of animals 
have protected their herds against the sources of infection when sur- 
rounded with widespread epizodtics. Whole countries have been kept 
free from certain maladies by enjoining the same methods, as shown 
in the absence of rabies in Australia. This was accomplished by 
prohibiting the entrance of dogs until after they had been quarantined 
for a sufficient time. The eradication of infectious diseases by holding 
rigidly and simply to the guarding of the channels of dissemination 
and infection has been accomplished a number of times on a large scale 
as instanced by the eradication of contagious pleuro-pneumonia in 
cattle from this country and from Great Britain. The elimination of 
foot-and-mouth disease in 1902 and again in 1908 are striking illustra- 
tions of efforts in this direction. The eradication of infectious diseases 
from individual herds is being accomplished repeatedly by adhering 
to the same methods. The Bang method of handling bovine tuber- 
culosis, as already mentioned, enables one to protect the well animals 
and to save all there is of value in the others. 
The isolation of the well from the sick and the thorough disinfection 
of the houses and yards containing the sick has resulted in stopping 
many outbreaks of disease. This is followed very generally even 
where vaccination and serum prevention treatment are resorted to. 
Several times in the writer’s experience success in checking the spread 
