300 The Philippine Journal of Science 1913 



ditions. All 6 of the men who ingested encysted Entamoeba 

 histolytica without neutralizing the acidity of the gastric juices 

 became parasitized. 



The incubation period of the parasite, that is, the period of 

 time elapsing between the ingestion of the infectious material 

 and the appearance of the entamoebse in the stools, is, as shown 

 in these experimentally parasitized men, from one to forty-four 

 days, with an average of nine days. In one case, man 44, in 

 which microscopic examination of the stools was by an over- 

 sight not made between the sixth and thirty-third day. Enta- 

 moeba histolytica was not found on the sixth and was found on 

 the thirty-third day. If we exclude this case and that of man 

 5, who ingested motile entamoebse and who had an abnormallj' 

 long incubation period, forty-four days, the average incubation 

 period of the parasite would be 5.7 days, which is approxi- 

 mately the same as in the case of Entamoeba coli. It is probable 

 that the number of entamoebas ingested would in part account 

 for the considerable variation in the incubation period in the 

 different men. 



Of the 18 men experimentally parasitized with Entamoeba 

 histolytica, 4, or 22 per cent, have developed entamoebic dysen- 

 tery. Two of these cases, men 30 and 32, had only slight attacks 

 of dysentery, lasting one or two days, and recovered without 

 treatment. The other 2 cases, men 2 and 41, had more severe 

 attacks of dysentery lasting one or more weeks, and recovered 

 only after receiving ipecac treatment. One of the latter, man 

 2, had a relapse thirty days after recovery which persisted until 

 treated. 



The 4 cases of experimental dysentery were obtained with 

 material from 3 different sources and representing 2 distinct 

 strains of Entamoeba histolytica. Men 2 and 30 were infected 

 with entamoebse from the same individual, man A, who was 

 convalescent eighty-four days from a slight attack of entamoebic 

 dysentery of two days' duration. Man 41 ingested a strain of 

 Entamoeba histolytica coming originally from the same source 

 as in cases 2 and 30, but which had been passed through two 

 other men, 29 and 36, who did not develop and have not sub- 

 sequently developed dysentery, before being ingested by man 42. 

 Case 39 was obtained after the ingestion of a distinct strain of 

 Entamoeba histolytica, strain D, which came from a "contact 

 carrier" of Entamoeba histolytica without symptoms or previous 

 history of dysentery. 



The passages of the 4 strains of Entamoeba histolytica in these 



