NATURE OF THE BACTERIOPHAGE 149 



have discovered harmonize with this hypothesis, with this hy- 

 pothesis only, and none contradict it. 



Moreover, I should repeat that I have not formed any hypothesis 

 as to the species to which the ultramicrobe belongs. I have 

 called it Bacteriophagum intestinale, a name simply denoting its 

 characteristic property and the place where I first found it. Is 

 it a protozoan? Is it a bacterium? Does it belong to a kingdom 

 which is neither vegetable nor animal? Does it arise even in 

 another organism, a possibility which has been suggested in ex- 

 amining the first hypothesis? These questions can be ignored. 

 It is an ultramicrobe, a filtrable being endowed with the 

 functions of assimilation and of reproduction, functions which 

 characterize the living nature of beings and which pertain to 

 them alone. That is all that experimentation is actually able 

 to demonstrate. 



To try to penetrate further into its identity would be nothing 

 but purely speculative reasoning. 



EXPERIMENTAL PROOFS OF THE LIVING NATURE OF THE 

 BACTERIOPHAGE 



This section will, without doubt, be judged unnecessary by 

 the reader who has followed the experiments recorded in the 

 preceding chapters. However, it may be well to group these 

 proofs and to comment on certain experiments which can leave 

 no doubt, even in the minds of the most skeptical and uninformed. 



1. The bacteriophage proliferates, since serial cultures can be 

 continued indefinitely. In the action of the diastases there is 

 always a certain proportionality. The action is the more ener- 

 getic when the amount employed is large. With the bacterio- 

 phage this is not true. The activity is due to the quality of the 

 principle, not to its quantity, and this is, indeed, a property of 

 vital activity. A diastase acts in proportion to its quantity, a 

 bacterium in proportion to its virulence. 



2. The bacteriophage presents properties analogous to those 

 of other known living beings. Its resistance to agents of de- 

 struction, although great, is, however, less than that of many 

 organisms of which the living nature is unquestionable and 

 uncontroverted. 



