Contagious and Epizootic Diseases. 57 



II. IMMUNITY BY TONICS AND ANTIFEEMENTS. 



The \ise of tonics is based ou their tendency to pi'odnce 

 a more vigorous health. Like' good hygiene, therefore, 

 they will sometimes assist in warding ofE infection, or in 

 rendering the resulting attack more mild. A long course 

 of sulphate of iron will do much to fortify against lung- 

 plague, and is not without influence even on rinderpest ; 

 but a certain number of victims suffer after all, and too 

 often the plague continues to extend. 



The free use of sulphites, bisulphites, and hj'posulphites 

 was long ago shown by Polli to counteract the dangers of 

 inoculated septicasmia, and has undoubtedly the effect of 

 retarding the growth of certain disease-germs within the 

 animal body, but at best they but mitigate the disease and 

 do not prevent the progress of the infection to other 

 animals. 



III. IMMUNITY BY PASSING THEOUGH THE PLAGUE BY 



EXPOSURE. 



In a country where a deadly animal plague is generally 

 prevalent, a measure of security is sometimes secured by 

 passing the young and comparatively valueless through the 

 disease. Those that die are but a trifling loss, while the 

 survivors resist this plague for their whole life-time. This 

 has been especially adopted in lung plague. 



rv. IMMUNITY BY INOCULATION FKOM A MILD TYPE OE THE 



PLAGUE. 



Before the days of Jenner this was employed for small- 

 pox, and to the present time it is largely resorted to for 

 sheep-pox. Sheep in good health, inoculated from a mild 

 case of the disease, usually have the pox in a mild form ; 

 nearly all recover, and the flock is thereby preserved. 



