260 WALKER. 



The problem is primarily one of species, of the identity of the amoebae 

 that have been described by different authors in water, in cultures, in 

 stools of healthy persons, and in amoebic dysentery. Anyone who has 

 attempted to identify amcebse by the descriptions in the literature will 

 probably admit that species determination of the Amoebidae is in a chaotic 

 state. New species have repeatedly been established upon inconstant 

 variations. One stage in the life-cycle of an organism has sometimes 

 been described as one species and another stage as a second species. 

 Authors, failing to identify the amoebae in their possession with the in-' 

 complete descriptions in the literature, have established new species with 

 diagnoses as indefinite as those of their predecessors. 



The determination of species of protozoa, it is true, is difficult, not only 

 on account of the minuteness and the more or less complicated life-cycles 

 of these unicellular organisms, but also because cultural and biologic tests, 

 that enable the bacteriologist to determine species with a certainty second 

 only to that of the chemist in identifying the chemical elements, have 

 a limited application to the protozoa — ^how limited in their application to 

 the parasitic amoebae will be apparent later. Protozoologists, therefore, 

 are forced to rely chiefly upon morphological characters to determine 

 species. However, I believe such characters are adequate for the purpose, 

 if a proper discrimination be made between variable and constant charac- 

 ters and if all the stages in the life-cycle of an organism be taken into 

 consideration. Many of the most obvious morphological characters of 

 the vegetative, or trophozoite, stage of amoebae, such as shape, size, number 

 and shape of the pseudopods, extent of the ectoplasm and contents of the 

 entoplasm are classically variable ; on the other hand the characters of the 

 encysted stage are relatively constant and usually absolutely diagnostic : 

 yet the descriptions in the literature of most free-living and of many 

 of the parasitic species are based exclusively upon the trophozoite, while 

 the more constant and distinctive characters of the cyst have been wholly 

 neglected. It has been my experience in studying amoebae that, if the 

 characters of both the trophozoite and the cyst be taken into consideration, 

 they can always be separated into species having well-defiaed morpho- 

 logic characteristics. Therefore, it has seemed important to undertake 

 a careful comparative study of the amoeboid organisms found micros- 

 copically and culturally in the Manila water supply, in the stools of 

 healthy person, and in amoebic dysentery for the purpose of determining 

 the genera and species represented, their parasitism, their cultivability on 

 artificial media, and their relation to amoebic dysentery. 



REVIEVS^ OF THE LITBEATURE. 



Entamoeba coli (Loesch) Schaudinn, 1903, is generally considered to be the 

 amoeba first observed by Loesch in a case of dysentery at St. Petersburg in 1875. 

 It was carefully described by Casagrandi and Barbagallo in 1897. Schaudinn 

 distinguished it from a pathogenic species, Entamosba histolytica, in 1903 and 



