260 PARASITIC BACTERIA. 



The human diseases diphtheria, lock-jaw, bubonic plague, cholera, 

 and hydrophobia have either been mastered or at least mitigated 

 by discoveries that have come from the study which Pasteur started ; 

 while among animals at least two diseases are controlled by prevent- 

 ive inoculation anthrax and black leg. Some success also has 

 attended similar methods with tuberculosis. 



MICROORGANISMS THE CAUSE OF DISEASES. 



The studies of the last twenty-five years have demonstrated that 

 the majority of diseases in animals and plants are produced by the 

 growth of parasites of some kind, and mostly by what may be called 

 microorganisms. Bacteria, yeasts, and molds are all concerned and, 

 in addition, some diseases are produced by microscopic animals. 

 The subject of germ diseases has become one of very wide range 

 and cannot be considered to any great length in this work. The 

 discussion of such diseases among animals belongs to veterinary 

 medicine, and of those among plants to botany. In our general 

 consideration of microorganisms as related to agriculture, we can 

 review only the important principles involved, and give a brief 

 survey of the more important diseases. 



