VIRULENCE OF THE BACTERIOPHAGE 101 



the thousandth tube of the series is represented, in cubic kilo- 

 meters, by the figure 10 3982 . To appreciate this incommensurable 

 figure, it is sufficient to say that with only the twenty-second 

 passage, one drop of the original filtrate taken from the feces has 

 been diluted in a number of cubic kilometers of liquid expressed 

 by the number 10 70 . That is to say, by a number of which the 

 logarithm has for a characteristic 70; which would be a cube of 

 liquid of such size that it would require a billion centuries for 

 a ray of light to pass through from edge to edge. 2 



The action is not, therefore, to be explained as a persistence 

 of anti-typhoid bacteriophagous germs through a series of suc- 

 cessive cultures. 



According to the conception of Maurice Nicolle a bacterium 

 may be considered as a mosaic of properties. Each of these 

 properties: resistance to heat, vitality, virulence for such and 

 such an animal, etc., is susceptible, within a single individual, 

 of continuous variation. Within a bacterial culture, and at 

 any given moment, no two individual bacteria can be found 

 possessing exactly the same properties. This conception, demon- 

 strated by daily experience, applies moreover to all living beings. 



Variation, that is, the property of adaptation, is an attribute 

 of life and of life exclusively. Like all living beings, the bacterio- 

 phage adapts itself continually, and in any culture the ultrami- 

 crobes which compose it do not all possess exactly the same prop- 

 erties. Some are susceptible of rapid adaptation toward a given 

 bacterium, others toward another organism. A bacteriophagous 

 ultramicrobe is a mosaic of properties. 



2 It is evident that the same mathematical reasoning demonstrates that 

 the bacteriophage is itself a living being. If one would wish to explain 

 lysis as due to the presence of a lytic diastase in the intestinal contents 

 (or, what actually amounts to the same thing, the presence of a co-ferment 

 or a catalyzer in the intestinal tract capable of activating a pro-diastase 

 contained in the bacterium), the diastase or the catalyzer or the co-ferment 

 would be quickly eliminated by the dilution. If we suppose possible the 

 persistence of one of these principles, in spite of the dilution which approxi- 

 mates infinity, and its presence at each point in an incommensurable 

 amount in the liquid, we are endowing this principle with the metaphysics 

 of ubiquity. Any conception of transmissible serial bacteriolysis which 

 does not admit as the origin of the phenomenon an autonomous living 

 being, ends in a mathematical absurdity. 



