30 



" Shiga bacilli, Flexner bacilli. Hiss Y type of Flexner bacilli, and 

 " also a strain of B. coli communis which was unattacked by the 

 " original filtrate." He further remarks that, in consequence of 

 these observations, which were made by Wollstein, " we have 

 " been able, by a method of successive passages through appro- 

 " priate strains, to extend the lytic power to other species, as 

 " typhoid and paratyphoid bacilli, and have obtained by this 

 " somewhat different technique results similar to those recently 

 " published by Bordet and Ciuca." 



I think the point of special importance in the above observa- 

 tions is that the transition from the lytic principle (a), which 

 acts only on its own strain, to the wider lytic influence (6) is 

 effected without the introduction of any new factor. It is simply 

 the result of the continued action of a, which first produces rela- 

 tively resistant forms of the original strain and then, by attacking 

 and breaking down some of these resistant forms, gives rise to 

 the wider lytic principle 6. This means, expressed in terms of 

 the hypothesis which I am advocating, that the synthesis of the 

 bacterial protoplasm is interrupted more readily, or at an earlier 

 stage, in the case of the normal bacillus than in the case of the 

 resistant form ; with the latter, synthesis has gone a little further 

 before the lytic principle succeeds in producing its disintegrating 

 effect, and, consequently, the products of disintegration are 

 different. 



From this point of view one may attempt to throw a little 

 light on the puzzling question, Why are there such remarkable 

 differences amongst what I may term " pure " lytic principles, 

 which are derived from different strains of the same bacterial 

 species ? By " pure " I mean that each is derived ab initio from 

 a particular strain of the species and has not been subjected to 

 any external modifying influence, such as passage through another 

 strain of the species or through a strain of another species. I 

 think the explanation, at least in part, is to be referred to the 

 extreme complexity of protoplasm, owing to which very slight 

 differences in its stability, or in the particular arrangement of its 

 constituent parts, at the critical phase of bacterial growth, may 

 result in disintegration products possessing different lytic 

 activities. 



I think it is desirable first to recognise such possible com- 

 plexities of a single species, before embarking on still more 

 complicated problems such as (1) Why is a " coli " lytic principle 

 altered when it is transmitted through a culture of a different 

 species, such as Shiga, or (2) Does transmission of lytic principles 

 through different representatives of intestinal bacteria bring out 

 evidence of " group " relationship and different degrees of 

 kinship ? 



Here is another interesting study which throws some light on 

 " lytic principles," because the experimental conditions are not 

 too complicated. It is concerned with the end results which are 

 obtained by continued exposure of bacteria to a lytic agent. 



