VIII, B, 4 Walker and Sellards: Entamcebic Dysentery 275 



In consequence of the failure in every case to find the amoebse 

 microscopically in the stools of the men who had ingested cul- 

 tures of amoeba and the ability to recover them in cultures only 

 during the first few days after the ingestion, it is probable, as 

 Werner (1908) and later one of us, Walker (1911), have con- 

 cluded, that the cysts of the ingested amoebse pass unchanged 

 through the intestinal tract and find conditions suitable for devel- 

 opment when the faeces are placed on the culture medium. In 

 the case of experiments X and XVI, in which only motile amoebae 

 were ingested, the use of magnesium oxide to neutralize the 

 acidity of the contents of the stomachs of the men may have 

 favored the existence of the amoebse in their passage through the 

 intestinal tract of these men. It is also possible that the amoebse 

 became encysted (a protective reaction that takes place under 

 any unfavorable conditions) in the intestines of these men. The 

 failure to recover in cultures of the stools 3 strains of species 

 A, fed five times, indicates that the cysts of this species are ordi- 

 narily incapable of withstanding passage through the human 

 stomach. 



Therefore, in consequence of our failure to parasitize men in 

 20 ingestion experiments with 13 strains of 8 species of amoebse, 

 we believe that the conclusion reached in the morphological study 

 (Walker, 1911), that the cultivable amoebse are not capable of 

 living as parasites in the human intestine, is experimentally 

 proved. 



Following the feedings with the cultivable amoebse, one man 

 (experiment XIV) who had ingested a culture of Amoeba G, 

 isolated from a diarrhoeal stool in Kansas, United States, out- 

 side of the endemic region, developed a slight attack of dysentery 

 of two days' duration, thirty-five days after feeding. Amoeba G 

 ingested by this man was recovered in cultures on the first and 

 second days after feeding and never afterward. It could never 

 be found microscopically in the stools of this man. Two other 

 men (experiments XV and XVI), who ingested the same strain 

 of amoeba, showed a similar behavior of the amoeba, but did not 

 develop dysentery. On the other hand, the amoeboid organism 

 found in the stools of the man in experiment XIV during the 

 attack of dysentery belonged to a species and genus (Entamoeba 

 histolytica) distinct from the organism ingested by this man. 

 It could not be cultivated on Musgrave and Clegg's medium, but 

 was demonstrable microscopically in the stools during, and sub- 

 sequent to, the attack of dysentery. Moreover, Entamoeba his- 

 tolytica from the stools of this man has been used to infect 



