STATUBE AND CAUSE OF HOG CHOLEEA 



from taking stains that render bacteria more 

 plainly visible. The virus readily passes porce- 

 lain and infusorial earth filters which retain all 

 visible bacteria, but it is itself retained by the 

 finest porcelain filters. It does not pass through 

 colloid membranes. In the human subject, mea- 

 sles, mumps, scarlet fever and smallpox are among 

 the diseases caused by filterable viruses, while 

 among animals rinderpest, foot-and-mouth dis- 

 ease and rabies are some of the diseases that fall 

 in the same group. The classification is a rather 

 loose one, being based entirely on the fact that 

 these viruses will pass filters that retain visible 

 bacteria, rather than on morphological or cultural 

 characteristics. 



There is no conclusive evidence that hog cholera 

 virus has been propagated outside the bodies of 

 infected swine. After a hog has been exposed to 

 the disease and actually infected, the virus ap- 

 pears in the blood stream in about four days, and 

 thus all vascular organs harbor it during the at- 

 tack. In the later stages of a few chronic cases, 

 we have found the blood free of the virus, but we 

 do not know whether this is the rule, nor is there 

 definite knowledge of the part played by " car- 

 riers " in harboring it. It is eliminated through 

 the excretions. The urine is regularly infectious, 

 the feces may or may not contain it, and the dis- 

 charge from the eyes and skin ulcers is infectious 



