Aug. 19, 1922] THE BACTERIOPHAGE. [ MrlrclXT; .. 



strain of bacteriophage one can vary experimentally this intensity. Variability 

 is an essential characteristic of life. 



We have seen, first, that of all the possible hypotheses concerning the 

 nature of the bacteriophage, the hypothesis of an ultramicroscopic parasite of 

 bacteria is alone admissible. Moreover, we have just seen that this hypothesis 

 is not contradicted by any of the facts of bacteriophagic phenomena; and, 

 furthermore, all of the facts cannot be explained if this hypothesis is aban- 

 doned or modified. It follows logically, therefore, that such a hypothesis be- 

 comes a certitude. 



Further, I would remark that I do not specify in any way the species to 

 which the ultramicroscopic organism, which I have given the name of Bac- 

 teriophogtwi intestinole, belongs; the name simply recalls its characteristic 

 property and the place where it was at first found. Is it a protozoon, a fungus, 

 a bacterium? Does it belong to a kingdom which is neither the vegetable nor 

 the animal— a still simpler form of life than any which we at present know? 

 These are questions which cannot at present be answered. All that we know 

 of it is that it is an ultramicroscopic organism, a filtrable being, parasite of 

 bacteria, endowed with functions of assimilation and reproduction— functions 

 which characterize the living nature of the being which possesses these proper- 

 ties. That is all that experiment actually shows us.* 



The foregoing discussion can only apply to the phenomenon of bacteriolysis 

 in series presenting the special characters that I have indicated. This being so, 

 a final question arises— that of the plurality of the serial phenomena. 



In 1915 Twort^- described a bacterial transformation taking place in series, 

 under the influence of a principle which passes through porcelain filters. His 

 researches have been made chiefly with a micrococcus isolated from vaccine. 

 In addition he observed an identical phenomenon with two other bacteria— a 

 large indeterminate bacillus, and a bacillus of the coli-typhoid group. Twort 

 isolated the active principle in the following manner. 



"Some interesting results, however, were obtained with cultivations from 

 glycerinated calf vaccinia. Inoculated agar tubes, after twenty-four hours at 37°, 

 often showed watery-looking areas, and in cultures that grow micrococci it was 

 found that some of these colonies could not be subcultured, but if kept became 

 glassy and transparent. On examination of these glassy areas nothing but minute 

 granules, staining reddish with Giemsa, could be seen." 



The transforming principle is contained in this transparent material. 



"The transparent material when diluted (one in a million) with water or saline 

 was found to pass the finest porcelain filters with ease, and one drop of the filtrate, 

 pipetted over an agar tube, was sufficient to make that tube unsuitable for the growth 

 of the micrococcus. That is, if the micrococcus was inoculated down the tube as a 

 streak, this would start to grow, but would soon become dotted with transparent 

 points which would rapidly extend over the whole growth. If in an infected tube 



* I will mention, in passing, the hypothesis of Salimbeni: the enzymes would be secreted 

 by a myxobacteria, microscopically and even macroscopieally visible, given filtrable spores. 

 All the workers who have studied the question have failed to observe this would-be 

 myxobacteria, which besides, according to the description of Salimbeni, presents a mycelium 

 (?). That can only mean an impurity, as I have elsewhere pointed out. 



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