less so far as the sick are concerned, and it may be
worse than useless for those not yet infected. All animals suffering with
infectious diseases are more or less directly a menace to all others. They
represent for the time being manufactories of disease germs, and they are
giving them off more or less abundantly during the period of disease. They
may infect others directly or they may scatter the virus about, and the
surroundings may become a future source of infection for healthy animals.
This leads us to the subject of prevention as the most important of all
which claim our attention. In this place only a few general remarks will
suffice to bring the subject before the reader.

The most important thing is to keep disease away from a herd or farm. To do
this all sick or suspicious animals should be avoided. A grave form of
disease may be introduced by apparently mild or trivial cases brought in
from without. It is generally conceded that continual change and movement
of animals are the most potent means by which infectious diseases are
disseminated.

With some cattle diseases, such as anthrax, rinderpest, and
pleuropneumonia, preventive inoculation is resorted to in some countries.
This may be desirable when certain diseases have become established in any
locality so that eradication is impossible. It should not be practiced in
territories where a given disease may still be extirpated by ordinary
precautions. Preventive inoculation is applicable to only a few maladies,
and therefore its aid in the control of diseases is limited.

When an infectious disease has gained foothold in a herd the course to be
pursued will depend upon the nature of the malady. A good rule is to kill
diseased animals, especially when the disease is liable to run a chronic
course, as in tuberculosis. The next important step is to separate the well
from the sick by placing the former on fresh ground. This is rarely
possible; hence the destruction or removal of the sick, with thorough
disinfection of the infected locality, is the next thing to be done. As to
the disinfectants to be used, special directions are given under the
various diseases, to which the reader is referred. Here we will simply call
attention briefly to the general subject.

DISINFECTION AND DISINFECTANTS.

Disinfection consists in the use of certain substances which possess the
power to destroy bacteria or their spores, or both. Those which are
cheapest and most availabl