508 DISEASES OF THE HORSE. 
the germs may occur by inhalation, skin abrasions, wounds of any 
kind, through the genital organs, and at times also through the milk 
ducts of the teats. Asa general rule infectious diseases have a period 
of incubation which comprises the time elapsing between the expos- 
ure to the infection and the actual appearance of the disease. This 
period varies in the different diseases. 
The treatment of infectious diseases is, as a rule, unsatisfactory. 
When the symptoms have once appeared a disease is liable to run its 
course in spite of treatment, and if it is one from which animals 
usually recover, all that can be done is to put them into the most 
favorable surroundings. Many infectious diseases lead sooner or 
later to death; treatment is useless so far as the sick animals are con- 
cerned, and it may be worse than useless for those not yet affected. 
All animals suffering with infectious diseases are more or less directly 
a menace to all others. They represent for the time being manufac- 
tories 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 the future source of infection. 
Therefore, in the control of infectious diseases prevention is the 
most important procedure. The isolation or segregation of healthy 
animals from infected ones should be primarily considered, and if at 
any time an animal manifests the symptoms of an infections disease 
it is essential to protect the others from such a source of danger. In 
some of the infectious diseases it may become advisable to kill the 
infected animals in order to avoid the spread of the disease. This is 
especially important in diseases which are slow in their course, such 
as tuberculosis. At times when diseases appear in a country where 
they have not been prevalent it becomes advisable and necessary to 
protect the healthy herds by the slaughter of all the infected animals. 
Pursuance of this policy has resulted in control of the foot-and- 
mouth disease, and has proved to be a very satisfactory’ method of 
eradication. 
DISINFECTION. 
Disinfection is a very important phase in the control of infectious 
disease. This consists in the use of certain substances which possess 
the power to destroy bacteria or their spores, or both. The cheapest 
and most available for animal diseases are ordinary freshly slaked 
lime, or unslaked lime in powder form, chlorid of lime, crude car- 
bolic acid, corrosive sublimate, formalin, formaldehyde, gas, cresol, 
etc. 
In the disinfection of stables and premises it is essential to execute 
the work in a most thorough manner. This may be satisfactorily 
accomplished by carrying out the following directions: 
