LIFE'S FRINGES 



appears well-nigh unavoidable that the lysis of the bacteria is caused 

 by a living organism of ultra-microscopic size that multiplies during 

 the lytic process. 



For that matter, the study of various diseases of man, animals, and 

 plants had, already long before the discovery of the bacteriophage, 

 yielded the conclusion that the causal agents of these diseases, too, 

 were ultra-filterable living organisms. Also in these cases had the fact 

 been demonstrated that the contagious agent can pass through filters 

 that retain all microscopic micro-organisms; and it had been shown 

 beyond a doubt that during its activity this agent multiplies in its host 

 so that in this manner it may be propagated ad infinitum. 



The concept of the existence of an invisible world in the strictest 

 sense was strongly supported by the fact that shortly phenomena were 

 established that unmistakably seemed to point to adaptations or to 

 changes in the virulence of the types of virus studied. In short, these 

 agents behaved in every respect in a manner that is equally character- 

 istic of numerous parasitic microbes of microscopically observable 

 size. Attention had, however, been drawn to the fact that all these 

 virus types shared one common property, viz., their inability to multi- 

 ply in media devoid of normally observable living cells. But because 

 this property had also been encountered among some few microscop- 

 ically visible single-celled parasites, this observation did not necessarily 

 disturb the confidence in the ultra-microscopic living world. 



It is, however, self-evident that already at an early date the desire 

 was felt to demonstrate more directly the corpuscular nature of the 

 contagious agent present in a filtrate. A few years ago the British 

 scientist, Barnard, succeeded in doing so with the aid of a highly per- 

 fected technique. He prepared photomicrographs with monochrom- 

 atic ultraviolet irradiation and quartz optics. The consequent increase 

 in resolving power made it possible to obtain images of certain virus 

 types on the photographic plates. If one examines the reproductions 

 of these images, e.g., of the smallpox virus, the ectromelia virus of 

 mice, and Kikuth's canary virus, and compares them with identically 

 prepared photomicrographs of a small bacterial species such as B. pro- 

 digiosum, one fails to find grounds for protesting against a concept that 

 considers these viruses as diminutive 'editions' of known microscopic 

 parasites. Hence it might have appeared to many persons that the 

 microbiologist had found his theoretically probable world of ultra- 



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