508 DISEASES OF THE IIOBSE. 



the germ? may occur by inhalation, skin abrasions, wounds of any 

 kind, through the genital organs, and at tiniej> also through the milk 

 ducts of the t^ats. As a 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 

 ])eriod varies in the different diseases. 



The treatment of infectious diseases is, as a rule, imsatisfactory. 

 When the symptoms have once appeared a disease is liable to run its 

 coui"se in spite of ti'eatment, 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 

 lat^r 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 loss 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 tliey 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 infectious 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 coimtry where 

 they have not been prevalent it becomes advisjible and necessiiry 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 subst^inces 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 : 



