16 



Bordet thinks that it is an autolytic enzyme produced by 

 the bacteria which undergo lysis and that it is due to " a 

 nutritive vitiation primarily started by external influences, 

 an example of which may be the contact with a leucocytic 

 agent." Bail has suggested that it consists of minute 

 particles of the bacteria themselves and that these particles 

 will live and multiply, not independently but when provided 

 with nutrient material from living bacteria. Otto and 

 Winkler regard it not as a living virus but as composed 

 of minute fragments of bacterial protein, arising from the 

 disintegration of living bacteria and endowed with the 

 properties of enzymes. This stage is characterised by 

 controversies between upholders of conflicting theories and, 

 generally, by the assumption that the " Twort-d'Herelle 

 phenomenon " is an entirely new discovery and differs 

 from previously observed factors concerned with bacterial 

 variation. 



(4) Since then a reaction has set in. More attention 

 has been paid to the fact that " lytic substance " is not 

 merely an agent which destroys bacteria ; it is also a means 

 of producing bacterial variants. Moreover, it has often 

 been found that some of these variants closely resemble 

 variants described long ago, before " lytic principle " was 

 discovered. Further, it is suggested that "lytic principle " 

 is not a new discovery but simply a revival — supported by 

 new experiments — of old ideas and observations about the 

 lytic properties of bacterial enzymes ; and the balance of 

 opinion seems to be definitely against d'Herelle's view that 

 it is attributable to a living virus which acts as a 

 " bacteriophage." 



For my own part, I agree to a large extent with phase (4). 

 In particular, I think that " lytic phenomena " are closely 

 associated with other facts about bacterial variation where lysis 

 may not be demonstrable, and that the former should be considered 

 in conjunction with the latter as part of the same general problem. 

 But, whilst it is desirable to link up new work with old, wherever 

 it is possible to do so, I would not go so far as to suggest that 

 " lytic substance," which acts only on living and actually growing 

 bacteria, may be identified with those previously known bacterial 

 enzymes which are much less restricted in their sphere of action. 



In concluding this note, I may give a few references for 

 readers who desire a fuller historical account. Penfold (Journ. 

 Hyg., xi-xiv, 1911-14) has written extensively on bacterial 

 variants and has suggested changes in the enzyme chemistry of 

 the bacterial cell as an explanation of his observations. Arkwright's 

 article (Journ. Path. & Bad., xxiv, p. 36, 1921) is important; 

 it describes his observations on " rough " and " smooth " 

 colonies and brings them into line with other investigators' work 

 on mutation. The question of the " lytic principle " was discussed 

 at the last meeting of the British Medical Association and is 



