CHAPTER XXXIX 

 FILTERABLE VIRUSES^ 



THOMAS M. RIVERS 



Rockefeller Institute for Medical Research 



New York City 



For various reasons, many morbid conditions are now referred to as "filterable 

 virus diseases." Certain of these conditions are claimed to be caused by bacteria, pro- 

 tozoa, spirochetes, or self-propagating inanimate substances. Inasmuch as the claims 

 have not been generally accepted, one may consider that the etiological agents of the 

 majority of these diseases are still unknown. Since there is a possibility that many of 

 the agents are not ordinary bacteria, no imperative reason is apparent for discussing 

 them in a book on bacteriology. Nevertheless, the contagious nature of many of the 

 diseases makes it advisable for investigators interested in infection and immunity to 

 be acquainted with certain important facts concerning them. 



In Table I are listed most of the diseases which are included by different observers 

 in the group under discussion. The etiological agents concerned in these diseases, or 

 groups of them, have been given a variety of names, e.g., "filterable viruses," "in- 

 visible microbes," "ultra-microscopic viruses," "infra-microbes," "protista," "micro- 

 plasms," "chlamydozoa," and "strongyloplasms." The results of a superficial exami- 

 nation are convincing that none of these names is apphcable to all of the etiological 

 agents. Names, however, facilitate the interchange of ideas between individuals. For 

 practical purposes, then, the term "filterable viruses," chiefly because of its wide us- 

 age, is as satisfactory as any name suggested. Throughout this chapter the terms "fil- 

 terable viruses" and "viruses" will be employed in a noncommittal way to desig- 

 nate active transmissible agents which are capable of producing pathological 

 conditions in bactetia, plants, insects, fish, birds, and mammals, and which by general 

 consent are more or less limited for the moment to the etiological agents of the 

 diseases listed in Table I. 



FILTERABLE VIRUS DISEASES 



The arrangement of the diseases in Table I is for convenience of discussion and 

 carries no taxonomic significance. In the first place, filterability of the etiological 

 agents does not sharply delimit this group of diseases, as it is well known that the 

 viruses share this characteristic with certain small bacteria and vibrios, and also with 

 some spirochetes and jjrotozoa. Furthermore, in regard to the etiological agents of 

 some of the diseases within the group, e.g., chicken-pox and herpes zoster, no filtration 

 experiments have been recorded. The viruses of still other diseases within the group, 



' Parts of this chapter were taken from a paper read by the author before the Society of American 

 Bacteriologists, Dec. 29, 1926, and later published in the Journal of Bacleriology. For a fuller dis- 

 cussion of the subject the reader is referred to the paper mentioned above and also to a book on 

 filterable viruses, to be published soon by Williams & Wilkins Co. 



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