FLUCTUATIONS: MUTATIONS: MODIFICATIONS 29 



despite its heresy, my opinion is that the majority — if not all — 

 of the last two are substantially of the same order. 



As fluctuations are designated those familiar variations in 

 one or other quality which distinguish the individuals of the 

 same sept or clan from one another. The various members of 

 the families to which each of us belong, while human beings, are 

 not identical, but vary within certain limits in height, breadth, 

 weight, length of arm, and so on. The various descendants 

 of a single individual, though they may approximate in these 

 particulars to the parents, vary from that parent in a very obvious 

 manner. Taken together the members of a tall family or strain 

 may, as a group, average above the normal, or of a stumpy 

 strain below the normal, but, with this, there is individual varia- 

 tion in height. And so it is with bacteria. With these fluctua- 

 tions we need not concern ourselves — they are in the strictest 

 sense individual : descendants placed in the same environment 

 need not exhibit them : a man 5 ft. 5 in. in height, for example, 

 marrying a woman of 5 ft. 1 in. may have children all of them 

 over 5 ft. 5 in. in height. 



By mutation we mean a very different phenomenon. From 

 causes we cannot as yet wholly fathom, a Shakespeare may be 

 the offspring of a country butcher : in a field of clover a plant 

 may show itself with quadripartite in place of tripartite leaves. 

 The same phenomenon is to be observed among bacteria, but 

 studying these forms devoid of sexual conjugation, the question 

 is whether we deal with one or two orders of events. Let me 

 give an example to the point. It has been pointed out by Barber 1 

 that while the ordinary culture of Bacillus coli shows separate 

 short, stumpy bacilli, occasionally while examining smears from 

 such we encounter filamentous chains of cells. He points out 

 that all the bacilli have grown floating in the fluid medium : 

 all appear to have been subjected to the same influences, and 

 yet here and there a bacillus when it divides has its progeny 

 remaining united instead of floating away to lead an independent 

 existence. He found that by isolating a filamentous form and 

 breeding from it he could obtain a new race constantly showing 

 a filamentous arrangement, with cultural characters distinguish- 



1 Kansas University Science Bulletin, iv., 1907, No. 1. Only recently in the 

 British Medical Journal of June 16, 191 7, Mr. Ainley Walker has called attention 

 to the same phenomenon. 



