Studies in Pleomorphism in Ty])hMS and otlier Diseases. 531 



the particular disease. In each case the discoverer is, in my view, 

 both right and wrong. He is wrong in so far as he believes the 

 organism to be a simple bacterium responsible as such for the 

 production of the disease. And he is right in believing that his 

 organism is intimately associated with the disease, though he has 

 not yet learnt that his bacterium represents unly a phase in the 

 complex life-history of a parasitic fungus, or perhaps of a protozoon, 

 and as such cannot itself reproduce the disease. I refer here only 

 to typhus fever, as it is only in this disease that my evidence is as 

 ;^et approximately complete. And this brings me to my third 

 heading. 



The Eelationship of Filterable Viruses to 

 Non-Filterable Bacteria. 



Your President, when introducing me to this Society, referred 

 in graceful terms to my work on infective disease, and suggested 

 that my views are known not to be orthodox. He is right. I am 

 not orthodox, and am in fact frankly a heretic as regards the 

 etiology of the exanthemata. I do not believe in, and cannot 

 accept, the current teaching as to the causal agents of the diseases 

 I have studied — namely, cerebrospinal fever, typhus fever, scarlet 

 fever, measles, typhoid fever, and paratyphoid fever— and my heresy 

 is based on this simple fact, that it has so far proved impossible to 

 show tlmt any of these diseases can be produced in animals by 

 injection of pure cultures of the " bacteria " generally implicated. 



Now, in the case of typhus fever, I was able to show two years 

 ago that it is possible to cultivate from the filtered body fluids the 

 Diplobacillus exanthematicus of Eabinowdtsch, an organism which, 

 when fully developed, will not pass the fine bacterial filters em- 

 ployed. These experiments I have now repeated on a very large 

 scale, and am satisfied as to the accuracy of the observations. Full 

 details will be published elsewhere. It is sufficient here to say 

 that these human filtrates are highly infective, and that theii 

 injection into monkeys reproduces in these animals a disease in- 

 distinguishable from that produced by injection of the unfiltered 

 body fluids, and that from monkeys injected with the latter I am 

 now able to recover at will further infective filtrates, and from these 

 filtrates I am again able to recover the " bacillus " in question. 

 And I further find that in suitable media, such as acidified broth, 

 it is possible to force this " bacillus " to reveal its true nature 

 as representing merely a phase in the life-history of what appears 

 to be a parasitic fungus allied to the hyphomycetes. As the photo- 

 graphs will show, immistakable evidence suggesting a fungoid 

 nature reveals itself in the sporulating " bacilli," isolated spores 

 and mycelial-looking growth. 



2 2 



