862 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



serum is diluted with normal salt solution or with ordinary bouillon 

 (i to 10) and passed through either a Berkefeld or Chamberland 

 filter, the filtrate, though free from all visible microorganisms, still re- 

 tains the power to produce hog cholera by subcutaneous injection. 

 The disease which is produced in this manner by the filtered hog 

 cholera serum is identical in all respects with the disease produced by 

 the unfiltered serum and also with the disease as it occurs in nature. 

 The hogs which receive the filtered serum present the symptoms and 

 lesions of hog cholera. The disease set up in this manner is very 

 contagious and hogs which recover from the inoculation of filtered 

 serum are thereafter immune against hog cholera. By repeated 

 inoculation and filtration this virus may serve to infect successively a 

 large number of hogs. 



The invisible virus of hog cholera, in view of its ability to pass 

 through the Chamberland B filter, must be regarded as one of the 

 smallest of the filtrable microorganisms. It has never been cultivated 

 artificially, hence, aside from its disease-producing qualities, we have 

 little knowledge concerning it. We do know, however, that the virus 

 is quite resistant to such common disinfectants as carbolic acid and 

 bichloride of mercury and that it is quickly destroyed by a 3 per cent 

 solution of liquor cresolis compositus (U. S. P.) as well as by a 5 per 

 cent solution of antiformin. When preserved in sealed glass bulbs 

 in a cool dark place, the virus retains its activity for six months or 

 longer. Rabbits, guinea-pigs, and other small animals are entirely 

 insusceptible to inoculations of the filtered virus in amounts which 

 would prove fatal to hogs. 



The virus of hog cholera is known to be thrown off from the body 

 through the urine, the faeces and the eye and nose secretions. There- 

 fore any agency which would serve to carry a particle of dirt from in- 

 fected hog yards might be the means of disseminating the virus. As 

 many sick hogs find their way to the public stock yards through ship- 

 ment by rail, all stock cars and stock yards are to be regarded as 

 permanently infected. It appears to be impracticable to prevent the 

 spread of the disease by methods of quarantine and disinfection alone, 

 owing to the impossibility of enforcing such measures thoroughly. It 

 has recently been found that a protective serum against hog cholera 

 may be produced by "hyperimmunization." The process consists in 

 giving immune hogs large doses of blood taken from hogs sick of hog 



