76 



These same filters were tested with a bouillon culture of Staphylo- 

 coccus pyogenes aureus in a reverse manner to fig. 2. From three to 

 four hours were taken in passing 150 cc. of the bouillon culture 

 through each filter. The filtrates remained sterile after twelve days 

 in the incubator. 



The Berkefeld filters were rigged with the glass cylinders which 

 come with them and a vacuum was used. About four hours were 

 required to run 150 cc. of the bouillon culture through each filter. 



THE FILTRATION OF CERTAIN VIRUSES. 



Peripneumonia of cattle, rinderpest, foot-and-mouth disease, South 

 African horse sickness, exudative typhus of chickens, mosaic disease 

 of the tobacco leaf, yellow fever, epithelioma contagiosum of fowls, 

 hydrophobia, clavelee, and hog cholera have each been shown to be 

 due to a virus which passes the pores of certain porcelain and diato- 

 maceous filters which hold back the ordinary bacteria. 



With the exception of peripneumonia we know nothing of the 

 character of the infective agent in these filtrates, which by direct 

 microscopic examination and by cultural methods have yielded no 

 morphological entity. • ' 



The outlook for finding in the body fluids, the specific cause of any 

 one of these diseases, by the microscopes in present use is encouraging 

 as long as we can say that we have a filter which will not allow the 

 virus of the disease to pass, but which does allow the particles of 

 some test substance to be plainly seen in the filtrate. 



It is far more important to know what particular filter a certain 

 virus can not pass through than it is to know what brands of filter 

 it does pass through. Given a filter that will not permit the virus 

 of a disease to pass through its pores, and if on testing that filter 

 we find that we can put through it visible particles of some test sub- 

 stance, there is plenty of hope that the infective agent of that virus 

 may be visible with our present oil-immersion systems. 



On the other hand, if we can find a filter which will not transmit 

 particles of microscopic size and yet will allow the virus of a certain 

 disease to pass into the filtrate, we can not expect to see the individual 

 entities in the virus. 



Several factors influence the filterability of a virus, namely, the 

 kind of filter used, the character of the menstruum in which the 

 • virus is suspended, the degree of pressure or vacuum used, the amount 

 of time allowed to the process, the temperature, the motility of the' 

 particles, and other factors. Unfortunately, in the study of the 

 literature of the various filterable viruses we sometimes fail to find 

 exact data on all these points. 



