262 The Philippine Journal of Science isis 



sequent natural infection. The clinical symptoms of the para- 

 sitized men have been carefully noted, and whenever conditions 

 appeared to warrant a physical examination of them has been 

 made. The men who developed dysentery have been promptly 

 treated after the manifestation of typical clinical symptoms, and 

 all have been cured. 



Experimental infections with material such as has been de- 

 scribed are subject to certain limitations and sources of error, 

 as are all experiments made with other than pure cultures. Just 

 what these limitations and sources of error are in the present 

 case and how far they can be avoided or controlled is worth 

 considering at this point. In the first place it is to be noted 

 that the presence of other microorganisms in the material fed 

 can in no way interfere with the determination of the parasitism 

 for man of the different species of Amoeba and Entamoeba, since 

 they can be identified by their morphological characters in the 

 microscopic examination of the stools. Secondly, it is evident 

 that in feeding experiments with amoeboid organisms which 

 are not followed by the development of dysentery, the presence 

 of other microorganisms in the infectious material will not com- 

 plicate the results. Therefore, it will be possible to eliminate 

 the nonpathogenic species with certainty. Finally, only in infec- 

 tion experiments followed by the development of dysentery will 

 the presence of other organisms in the infectious material be 

 a source of error. In such cases the experiments uncontrolled 

 would not prove the specific amoeboid organism to be the primary 

 etiologic agent in the production of the dysentery. 



Feeding experiments that were followed by dysenteric symp- 

 toms might be controlled by feeding other men all of the bacteria 

 that could be cultivated from the infectious material on ordinary 

 and special media and under aerobic and anaerobic conditions. 

 This would eliminate everything but noncultivable organisms, 

 such as the filterable viruses. However, controls of these ex- 

 periments were available which made it unnecessary to under- 

 take the work involved in the bacterial cultures and which were 

 considered to be more efficient. It was found that in feeding 

 material containing the presumably pathogenic entamoebse not 

 all of the men become parasitized with the entamoebse. Such 

 individuals were equivalent to controls that had been fed not 

 only all of the cultivable but also any noncultivable microorgan- 

 isms that the infectious material might contain, and they have 

 been reserved as controls of the men fed at the same time with 



