434 



FILTERABLE VIRUSES 



has been designated the Salmonella group. It is now known that the cause of 

 most important fatal disease of swine is a filterable virus. 



This virus shows remarkable powers of resistance to external influences, thus it 

 can be kept for months in animal tissues. It is not destroyed by drying and with- 

 stands a temperature of 58C. for two hours but not one of 72C. for one hour. 

 Cell inclusions have been found in smears from the conjunctivas of hogs sick with 

 the disease. See Chlamydozoa. A very valuable prophylactic but not curative 

 serum is found in the serum of animals recovering from the disease or in those 

 immunized. 



There are many other diseases of this nature which are important among the 

 domesticated 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 55C. in a few minutes. 



