Contagious and Epizooiio Diseases. 87 



mals and the disinfection of their products will not ei-adicate 

 the disease from the locality. It must be also destroyed in 

 the soil as well, and fortunately this can sometimes be done 

 by thorough drainage, exposure to the air, and prolonged 

 and thorough cultivation. 



Most of the disease-germs heretofore discovered have been 

 cultivated in carefully secluded glass vessels, in animal 

 liquids (soups, etc.), or on semi-solid organic bodies (pep- 

 tonized gelatine, etc.), showing very clearly the possibility 

 of survival outside the animal body. On the other hand, the 

 history of certain animal plagues (Kinderpest, lung-plague, 

 glanders, small-pox) furnishes no instance of the outbreak 

 of the disease without a pre-existing case as a direct cause, 

 but gives numerous examples in which, after the immunity 

 of a given coiantry for a great length of time, a specific 

 plague has been imported from without and has thereafter 

 spread with almost unprecedented severity. In such cases, 

 even where the soil is favorable to the preservation and 

 multiplication of the germ, it is still necessary first to im- 

 plant the seeds, as it was necessary to go abroad for the 

 seeds of the thistle which now grows so luxuriantly in many 

 of our fields. 



It follows that, instead of abandoning all effort for the ex- 

 tinction of plagues, the germs of which can increase in the 

 soil, etc., we should avail of every means of excluding their 

 seeds from our shores, or, if they have already gained a 

 foothold, we should prevent them fi'om spreading and con- 

 taminating new soils, and thus multiplying the permanent 

 centers of infection. 



GENEEAL CHAIIACTEES OF THE MIOEOPHYTES CAUSmG DIS- 

 EASE. 



The germs that determine specific diseases in animals 

 nearly all belong to the lowest order of vegetable life, known 

 as, Bacteria, ScMzophytes, Schizomyoetes, or Microhia. As 



