THE INFLUENCE OF SYMBIOSIS. 85 



intestine, or that it may be formed in the bowel. Such observations have 

 now been repeated and amplified by so many authors that they have ap- 

 peared in some of the modern literature as proved facts. 



Since 1904 Musgrave and Clegg have been publishing the results of 

 researches bearing directly upon this subject. It was first brought 

 forcibly to our attention in the cultivation of amoebae, which we could 

 not accomplish in a satisfactory manner except in the presence of other 

 living microorganisms, nor has a larger experience and maintained 

 interest given any different results. From the first, the association of 

 bacteria and amoebae appeared to be very intimate and subsequent work 

 which has been published and need not be reviewed here, has demonstrated 

 some such association to be necessary for the propagation of amoeba 3 under 

 any circumstances but those of pure parasitism. As a result of more than 

 four 'years of this continuous work the following suggestions are offered: 



1. Amoeba 3 in any natural environment, whether outside or within the 

 body (excepting in certain liver abscesses and a few other situations), 

 lead a parasitic life in that they feed upon, or in some other way sustain 

 life by the presence and often if not usually at the expense of other 

 living microorganisms. 



2. This symbiosis, even when the parasites are in a very mixed bac- 

 terial environment, is more or less specific for certain elements of this 

 environment. 



3. This specific character of the symbiosis may be changed in artificial 

 media and the evidence points to the occurrence of such changes in nature. 



4. All the parasites present in any given environment — the intestine 

 included — are not in symbiosis with the same bacterium. 



5. If amoebae in symbiosis with a given bacterium, after introduction 

 into the intestines of animals, succeed in remaining and propagating 

 there, it is usually by a change of symbiosis to an organism which was 

 already present in the intestine. 



G. All amoebae which reach the intestines of animals in a viable condi- 

 tion, whether as spores or as encysted or vegetative parasites, probably 

 do so either in an active sjnnbiosis, or in a receptive condition for some 

 more or less special symbiosis. The question of proliferation in the in- 

 testine probably depends — at least at first — upon the maintenance for 

 a time of the old symbiosis or the ability to change to another one with 

 living microorganisms present in the bowel. 



7. During this primary stage of intestinal infection and so long as 

 the true bacterial symbiosis in maintained, it is probable that no particu- 

 lar harm is clone to the bowel, regardless of the source or variety of 

 amoeba? present. However, as soon as the tissue components or secretions 

 begin to influence the metabolism or effect other changes in this bacterial- 

 amoebic compound, it is not unreasonable to believe that return manifesta- 

 tion toward the tissues may become a property of the amoebic-bacterial 

 symbiosis, and that lesions of the bowel result. 



