Aug. 19, 1922] THE BACTERIOPHAGE. [ MEorcAfjL'jRNAL 



the transparent portion cannot be grown except on the micrococcus makes 

 it impossible to obtain any definite evidence on these points. There is this, 

 however, against the idea of a separate form of hfe: if the white micrococcus 

 is repeatedly plated out a colony from the last plates may give a good white 

 growth for months when subcultured at intervals on fresh tubes; eventually, 

 however, most pure strains show a transparent spot, and from this the trans- 

 parent material can be obtained once again. Of course, it may be that the 

 micrococcus was never quite free from the transparent material, or this may 

 have passed through the cotton-wool plug and contaminated the micrococcus, 

 but it seems much more probable that the material was produced by the micro- 

 coccus. Incidentally, this apparent spontaneous production of a self-destroying 

 material which, when started, increases in quantity, may be of interest in 

 connexion with cancers. In any case, whatever explanation is accepted, I do 

 not think my experiments definitely disproved the possibility of its being an 

 ultramicroscopic virus, because we do not know for certain the nature of such 

 a virus. If the transparent portion were a separate virus, it might be vaccinia, 

 or it might be some contaminating non-pathogenic ultramicroscopic virus, for 

 it is conceivable that whereas a non-pathogenic variety might grow on micro- 

 cocci or bacilli, a pathogenic variety might grow only in the animal it infects. 

 As the animal experiments were negative, there is no evidence that it is 

 vaccinia, although such a virus might lose its virulence when grown outside 

 the body. On the other hand, no evidence was obtained that it was a non- 

 pathogenic variety. On the whole it seems probable, though by no means 

 certain, that the active lytic material is produced by the micrococcus, and 

 since it leads to its own destruction and can be transmitted to fresh healthy 

 cultures, it might almost be considered as an acute infectious disease of micro- 

 cocci. 



I have now described my original experiments and conclusions, and I will 

 pass on to consider the views of other workers in this field. Where differences 

 of opinion exist the controversy has centred chiefly round the experiments 

 that have been carried out to determine the source and nature of the lytit 

 material. I have already pointed out that when this material is diluted and 

 filtered and pipetted on to a tube of medium just before inoculating the tube 

 with the micro-organism to be lysed, then the action starts at definite points 

 throughout the growth. Dr. d'Herelle obtained a similar result in his experi- 

 ments with dysentery bacilli, and he considers this a strong point in favour 

 of the view that the lytic material is a separate living micro-organism. I can- 

 not, however, for several reasons, agree that such experiments prove this. First, 

 it is well known, notably in the case of certain starches, that the diastatic 

 enzymes do not in every case dissolve up the grains evenly, but start at certain 

 points, causing pitting and erosion of the grains; at the same time some grains 

 are more susceptible to the enzyme than others. In this case no one has sug- 

 gested that the imevenness of the action proves the diastatic enzyme to contain 

 a living ultramicroscopic virus. I have noted also with bacteria that not only 



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