RABIES 365 



THE FILTERABLE VIRUSES. 



The first disease of which the virus was found to be capable of pass- 

 ing through the finest porcelain filter was that of foot and mouth disease 

 (LofBer and Frosch, 1898). 



The filter which is ordinarily used for testing for the passage of such 

 disease agents is the Berkefeld filter, one made of diatomaceous earth. 

 Of the infections belonging to man in which such a passage of blood or 

 serum through the pores of a porcelain filter, capable of keeping back 

 even such a small bacterial organism as that of Malta fever, but which 

 does not hold back their virus, we have the following: foot and mouth 

 disease, trachoma, molluscum contagiosum, vaccinia, variola, rabies, 

 typhus fever, measles, scarlet fever, yellow fever, dengue, Papataci 

 fever and poliomyelitis. 



There are many diseases of this nature which are important among the domes- 

 ticated animals, such as pleuropneumonia of cattle, African horse sickness and hog 

 cholera. The viruses of pleuropneumonia of cattle and poliomyelitis have been 

 obtained in artificial cultures. Some of these viruses seem related to bacterial 

 infections and others to protozoal ones. These viruses differ as to method of trans- 

 mission, pleuropneumonia of cattle being transmitted by inhalation, rabies and 

 vaccinia by the cutaneous atrium, hog cholera by ingestion and many of those sup- 

 posed to have protozoal affinities, as yellow fever, Papataci fever and horse sickness 

 by mosquitoes. 



As a rule these viruses are destroyed by a temperature of 55 C. in a few minutes. 



