370 THE NATURE OF EVOLUTION 



but the pi'operty of readily liberating the polar forces. 



Lysogenic bacteria, having the property to unfold the polypeptide 

 ■chain easily on the application of ultrav^iolet light, cannot produce 

 phage following the irradiation if the bacteria are not present under 

 the appropriate environment. For instance, a culture grown in yeast 

 extract and irradiated will produce phage and lyse if left in yeast 

 -extract, whereas it will not produce phage if suspended in broth after 

 irradiation. Again certain bacteria in a manganese deficient m.edium 

 -will not produce phage after irradiation, but if supplemented with 

 manganese after the irradiation the virus is produced. Furthermore, 

 the inducing effect of ultraviolet light is inhibited by visible light 

 (59). These evidences may show how important are the environmental 

 conditions even for the liberation of the polar forces. 



The so-called latent viruses may, in the majority of cases, be the 

 virus pattern lacking this polar forces. For example, almost every 

 TTian shares the pattern of herpes virus but the virus is developed only 

 after some febrile diseases or after heat application which may cause 

 the unfolding. As considered already, common-cold is a disease whose 

 main causative factor appears to be chilling, but sometimes chilling is 

 not sufficient to cause the disease ; only persons who are under an 

 appropriate condition seem to become common-cold following chilling. 

 Chilling is therefore comparable to the irradiation, and the peculiar 

 ■condition or X-factor in common-cold may be comparable to the yeast 

 extract in the case of phage production. Persons apart from the 

 peculiar condition may not catch cold even if exposed to chilling ; in 

 a similar way, bacteria suspended in broth may not produce the virus 

 even after the irradiation. 



If common-cold is a disease which occurs in such a m.anner, its 

 virus must be a fixed one and accordingly it must cause a long- 

 lasting imm;unity ; but no imm.unity appears to be left behind the 

 infection. This must be attributed to the virus structure tending to 

 readily liberate the active group which, if liberated, makes the cells 

 fall into a severe pathological state as in the case of herps virus, a 

 phenomenon comparable to that concerning the phage against which 

 bacteria can become immune but the bacteria are occasionally shocked 

 by the liberation of the active group. If a man carrying the pattern 

 of common-cold virus is chilled under a peculiar condition, the active 

 group of the virus will be unfolded resulting in the severe shock in 

 the cells in which the unfolding takes place, thus common-cold being 

 developed. 



The pathological symptoms designated iuflammation may be caused 

 by the liberation of the polar forces ; the liberation is caused not only 

 by microorganisms including viruses but also many other physical or 



