CH. X] SUMMARY 141 



present such an appearance rather than another. B. coli in 

 the peritoneal cavity in the case of ascites may take the form of 

 a diplococcus; in milk or in urine it may develop into a 

 dense network of branching filaments resembling 5. cwif Aram, 

 but these changes in form do not imply any obliteration of the 

 specific character of the organism itself. 



We have already referred in this connection {vide p. 38) 

 to the analogy of a regiment of soldiers at manoeuvres and 

 a mass meeting of miners at the pithead. The various military 

 formations assumed by the first are as characteristic as the 

 concentrically arranged crowd formed by the second — so much 

 so that an observer at a distance might from the appearance 

 of these "zoogleic forms" state with confidence the character 

 of the units composing them although too far away to identify 

 the latter. A crowd of pitmen on strike might, however, march 

 in military formation and a regiment of soldiers at a boxing 

 match take the form of a crowd concentrically arranged — each 

 reproducing, that is to say, the appearance regarded as typical 

 of the other. This would not indicate that the pitmen were 

 changing into soldiers or the soldiers into pitmen. It is true, 

 nevertheless, that the arrangement most frequently observed 

 in one or the other case does indicate a tendency on the part 

 of the individual unit and may, therefore, afford a clue to 

 its identification. The behaviour of a civilian under certain 

 circumstances may furnish evidence of a military training and 

 deserters from the colours are not infrequently recognised by 

 such means. In a similar way, the occasional assumption by 

 the bacillus of diphtheria of clubbed and branched forms, 

 while helping us to identify it, also provides us with a clue to 

 its mycelial ancestry (Kanthack and Andrewes, 1905). 



Many of the variations exhibited by bacteria do in fact, 

 represent steps in the evolutionary process by which, in 

 the past, they have become differentiated — the individual 

 organisms living over again, as it were, the life history of the 

 race. This would appear to be the explanation of many 

 variations in morphology (Chapter IV). Others again repre- 

 sent the advance along new lines of this same evolutionary 

 process, leading to further specialisation and differentiation. 



