VIII, B. 4 Walker and Sellards: Entamcebic Dysentery 279 



to variation. While 8 is the usual number, individual cysts con- 

 taining from 9 to 16, usually mingled with the 8 nuclear cysts, 

 are not uncommon. Therefore, it is believed that the entamoeba 

 found so commonly in the stools of healthy persons in tropical 

 and subtropical countries is of one species, Entamoeba coli 

 Schaudinn. It is unquestionably the common species in the 

 Philippine Islands. 



This entamoeba is distinguished from Entamoeba histolytica, 

 to be considered in part IV, by its porcelaneous appearance; 

 greater ref ractiveness ; more sluggish motility ; the possession of 

 a nucleus that is distinctly visible in the living entamoeba and 

 contains a relatively large amount of chromatin ; by the develop- 

 ment of cysts that are larger, more refractive, and contain 8 or 

 more, instead of 4, nuclei; and by their frequent occurrence in 

 the stools of healthy persons (compare figs. 3 and 4 with figs, o 

 to 8, Plate I). 



Among the numerous experimental infections with entamoebze 

 that have been attempted by various authors, the following were 

 made with entamcebse identified as Entamoeba coli. 



Schaudinn (1903) experimented with kittens and also parasitized himself 

 on two occasions by swallowing cysts of Entamoeba coli. In both of his 

 own infections the entamcebse were said to have persisted in his stools two 

 months. None of these experimental infections of himself or of kittens 

 were followed by the development of dysenteric symptoms. 



Craig (1905) made a large number of experiments on the pathogenicity 

 of Entamoeba coli, using kittens to which the faeces containing the entamcebje 

 were fed in milk or injected rectally. In some cases the injections were 

 repeated from five to ten times in the same cat. In none of these experi- 

 mental animals did symptoms of diarrhoea or dysentery develop. 



Wenyon (1912) attempted to infect cats with faeces containing cysts 

 of Entamoeba coli which were administered per cBsophagus and per rectum 

 in large doses. In no case were these experimental infections followed by 

 dysenteric symptoms. These same animals were subsequently infected 

 with "Entamoeba tetragena" and developed entamcebic dysentery. 



Craig (1913) quotes a personal communication from Creighton Wellman. 

 He attempted to infect 5 kittens by injecting rectally 4 to 5 cubic centi- 

 meters of faeces containing Entam(Bba coli. None of the animals developed 

 symptoms of dysentery, and no dysenteric lesions were found in their 

 intestines at necropsy about one month after injection. 



In our series of experiments 20 men have ingested Entamoeba 

 coli. The men employed were carefully examined before use 

 with reference to previous attacks of dysentery and to. present 

 parasitization with amoeboid organisms. A few of the men 

 gave a history of dysentery at some earlier period of their lives. 

 Cultures on Musgrave and Clegg's medium and microscopic 



