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XVI. — Studies in Pleomorphism in Typhus and other Diseases. 

 By Edward C. Hoet, M.D. 



{Read November 15, 1916.) 



When a few days ago I accepted the courteous invitation of your 

 Honorary Secretary to place some of my work before the Society 

 I did so with mingled pleasure and pain. The pleasure lay in 

 the opportunity of placing before this learned and ancient Society 

 certain observations on the morphology of so-called simple bacteria, 

 and the pain consisted in the fact that with the exception of what 

 I have to show you in typhus fever my work is not yet sufficiently 

 far advanced to justify any claim to finality. I was in fact not 

 ready for publication when your invitation arrived, but Mr. Martin 

 Duncan most generously came to my aid, and by dint of incessant 

 work has prepared the beautiful photographs which he will 

 show you. 



The three subjects I wish very briefly to touch upon, and which 

 the photographs will illustrate, are pleomorphism, the true botanical 

 position of certain of the so-called lower bacteria, and the relation- 

 ship of filterable viruses to non-filterable organisms. 



Pleomorphism. 



This word, signifying as it does merely multiplicity of form, is 

 often restricted to reputed mutation phenomena, supposed examples 

 of which are repeatedly cropping up in morphological studies. 

 On the whole the sum of experience appears to be against morpho- 

 logical mutation, though one or two distinguished biologists to-day 

 are wise enough not to deny the possibility of its occurrence. 

 With this variety of pleomorphism I am however not concerned 

 to-day. What I wish particularly to bring to your notice is a 

 very different kind of pleomorphism which can easily be studied 

 in both unicellular and multicellular organisms. It is no doubt 

 true that one would perhaps hardly use the term pleomorphism to 

 describe the different developmental morphological phases in 

 passing from the impregnated ovum to the full-blown frog. But 

 this is merely because we are here watching the development of 

 the individual over considerable periods of time. On the other 

 hand, in the case of unicellular organisms with a complex life- 



