Studies in Fleomorphism in Typhus and other Diseases. 529 



history where perpetuation of the race takes place so rapidly that 

 we can see many of the phases represented on a film at any given 

 moment, it is perfectly accurate to speak of pleomorphisra, so long 

 as one makes it clear that one is not referring to genuine mutation 

 phenomena — if such there be. The Protozoa and the parasitic 

 fungi supply excellent illustrations of my point. 



The True Botanical Position of Bactekia. 



This use of the word pleomorphisra leads naturally to my 

 second heading, the true botanical position of the so-called simple 

 bacteria, and I will summarize what I have to say on this subject 

 in the form of this question : Are we justified in assuming, as 

 many of us do, that some of the lower forms of bacteria — to use a 

 text-book phrase — are really what they seem ? Are we certain that 

 there exists any form of living thing, however lowly, condemned 

 for countless ages, past and future, to reproduce itself exclusively 

 by the simple process of (transverse) division into two equal parts ? 



Our experience of comparative biology is wholly opposed to 

 the reasonableness of such a view, even when held by bacterio- 

 logists of repute who believe that a coccus or a bacillus can 

 only reproduce itself as a coccus or a bacillus, and who pin 

 their faith on the unconvincing observation that it will remain 

 true to type under standard cultui'al conditions in the labora- 

 tory. Now, in my belief, it is just because the confectionery 

 of the laboratory — to borrow from Sir William Collins' well- 

 stocked armoury — is more or less standardized, as compared witli 

 the unstable, ever-shifting culture media presented by infected 

 tissues, that we have gone astray in this matter. And it is 

 precisely this which originally led me, as doubtless it has led 

 others, to careful morphological and cultural study of certain 

 micro-organisms in their natural milieu — the infected tissues them- 

 selves, blood, cerebrospinal fluid, and so forth. The story is too • 

 long a one to tell here, but this at least I may say, with con- 

 fidence, that if you wish to determine the true botanical position 

 of a pathogenic " bacterium " you will in the first place often find 

 it necessary to use the body fluids themselves as the optimum 

 culture media before attempting its study in synthetic products. 

 And even then you will have often to use unaccustomed methods of 

 ^cultivation in order to avoid error. 



I must not, however, go here into details of technique, and 

 will only remind you that recent research has shown us that 

 many of the so-called bacteria have now been definitely proved 

 not to be bacteria at all, in the limited sense above defined. 

 Familiar examples are to be found in the streptotricha and sporo- 



Dec. 30th, 1916 2 o 



