90 THE DISEASES OF DOMESTIC ANIMALS. 



While many forms of fungus-life are known to have an eco- 

 nomical value, which we make practical use of in the production of 

 wine, beer, vinegar, yeast, etc., it is still more important to us, and of 

 no less practical value, that we should know the nature of the action 

 of those which produce disease, either in ourselves or in our domes- 

 tic animals. In both instances we have to do with questions of 

 natural economy, though the directions in which we pursue our in- 

 vestigations are so manifestly different. 



While much has been written upon the action of bacteria as re- 

 gards their etiological relation to disease, still we are forced to admit 

 that the subject is yet buried in the greatest obscurity. We find it 

 a hard task to distinguish the essential from the unessential in our 

 studies. 



The task we have before us is, then, to discuss the role which 

 bacteria play in the generation of disease in the animal kingdom. 



The diseases w^iich have been attributed to germinal action are 

 very numerous ; in fact, the list includes all the infectious and con- 

 tagious diseases, and many of a questionable character. Some en- 

 thusiasts (Hallier, Zurn, and others) have even professed to discover 

 the specific germ in every case, and we have in their writings most 

 explicit descriptions of the peculiar fungi of glanders, cholera, hay- 

 fever, rinderpest, and numerous other diseases, observations which 

 the most exact experiments of other equally proficient authorities 

 have failed to confirm. 



While our knowledge of specific disease-producing bacteria is 

 thus limited, we can safely assert that, with increasing years and 

 consequent improvement in the means and methods of investiga- 

 tion, it will be constantly extended and augmented. 



It is well known that there are forms of fungus-life which live 

 upon plants. A peculiar fungus — ustilago maidis — is the specific 

 cause of the rust of grain. It is also known that during one period 

 or form of its existence, this fungus lives upon the leaves of the 

 barberry-bush ; and practical experience, based on this knowledge, 

 has proved that with the removal of these bushes in certain districts 

 the sequential disease of corn has ceased to appear. 



A very important question is, Are the infectious elements of 

 disease of a gaseous nature, or are they organisms ? 



We know from experimental experience that a very small quan- 

 tity of infectious material is necessary to produce certain diseases. 

 We also know that, when in case of a certain disease (anthrax) we 

 introduce the smallest quantity of material into the organism, a mul- 

 tiplication of this material takes place. 



