THOMAS M. RIVERS 521 



virus even after repeated passages in man. Observations of a similar nature have been 

 made in regard to other virus diseases, e.g., contagious epitheHoma of chickens and 

 pigeons, and mosaic disease of tobacco and cucumbers.' Whether it is correct to speak 

 of these phenomena as examples of mutation is not known. In any event, when vi- 

 ruses are adapted to alien hosts, their characteristics are frequently altered, as well 

 as those of the diseases produced by them. 



CULTIVATION OF VIRUSES 



Following the discovery of the first filterable virus thirty-four years ago, numer- 

 ous workers claimed to have successfully cultivated in vitro, by means of simple or 

 complex media, one or more of these active agents. The term i)i vitro will be avoided 

 as there is no agreement in regard to its exact meaning. Therefore, the cultivation of 

 viruses in the presence or absence of living cells will be discussed. 



There is no reason to doubt that vaccine virus, herpes virus, typhus-fever virus, 

 the virus of Rous's sarcoma, and the virus of Rocky Mountain spotted fever have 

 been successfully cultivated in the presence of living cells in tissue cultures.^ More- 

 over, Levaditi-' has stated that the virus of poliomyelitis either survived or multiplied 

 in fresh spinal ganglia (monkey) placed in plasma. Harde^ was able to grow vaccine 

 virus in the presence of living corneal cells, but if the cells were killed by freezing or by 

 hypertonic salt solution the virus failed to multiply. The virus of fowl plague^ is cited 

 as one that has been cultivated in vitro. One might ask, however, if it has been culti- 

 vated in the absence of living cells, inasmuch as a large amount of blood was added to 

 the medium employed. Furthermore, Landsteiner and Berliner' found that the virus 

 would not multiply if laked or frozen blood was used, and definitely stated in their re- 

 port that one could not say that growth of the virus had taken place in a lifeless me- 

 dium. The statement is frequently seen that Bordet cultivated the etiological agent 

 of contagious epithelioma of chickens. Such statements are incorrect. Bordet" 

 claims to have cultivated a small bacterium which causes avian diphtheria. Further- 

 more, he specifically states that the bacterium does not cause contagious epitheli- 

 oma and that avian diphtheria and contagious epithelioma are two distinct diseases 

 in spite of the view held by some investigators. 



The majority of the attempts to cultivate the viruses have been unsuccessful. No 

 worker has proved that any of the etiological agents of the diseases in the table down 

 to mumps are susceptible of cultivation in the absence of living cells. ^ A satisfactory 

 explanation of the difficulty experienced in cultivating the viruses on artificial media 

 is not easily found. Their small size alone should not necessarily make them insus- 



' Walker, M. N.: Phytopatli., 16, 431. 1926. 

 ^ Meyer, E.: Arch.f. exper. Zcllforsch., 3, 201. 1Q26. 

 3 Levaditi, C: Compt. rend. Soc. dc bioL, 75, 202. 1913. 

 iHarde, E. S.: Ann. de I'Inst. Pasteur, 30, 299. 1916. 

 sMarchoux, E.: Compt. rend. Acad, de sc., 147, 357. 1908. 



'Landsteiner, K., and Berliner, M.: Ctntralbl. f. BaJitcrioL, Abt. I, Orig., 67, 165. 1913. 

 1 Bordet, J. : loc. cil. 



* Dr. Noguchi's report concerning the etiological agent of trachoma has appeared since the con- 

 struction of this table. 



