88 RESEARCH IN PROTOZOOLOGY 



worked out in great detail as yet but the L.E.S. medium of Boeck 

 and Drbohlav (1925) with its modifications is invaluable. 



(3) Evidences of host-parasite rigidity or transferability based 

 on animal transfer experiments. 



(4) Comparison of the pathological results produced by the 

 parasite in the natural host and in the hosts to which the parasite 

 has been experimentally transferred. In this respect a common 

 animal in which the pathological conditions can be compared or 

 standardized is important, e.g., the kitten is so susceptible to acute 

 amoebiasis that this animal has come to be recognized as a standard 

 animal for the study of acute amoebic infection. 



Most new species names which have appeared in the literature 

 have commonly been given without the application of the above 

 standards of species differentiation. As a matter of fact, it has be- 

 come quite the habit of some protozoologists of late to name 

 new species of protozoa, even when their morphology is identical, 

 purely on the basis of their being found in a host from which they 

 have not previously been reported. This is particularly noticeable 

 with reference to the Endania'ba which forms eight nucleate cysts 

 and resembles Endamwba coli in man. An amoeba of this type has 

 been found in man, several species of lower primates, several 

 species of rats and mice, the rabbit, the guinea-pig, the cow, the 

 domestic pig, the ground squirrel, the goat and sheep. In most 

 cases new species names have been given to these amoebae and 

 these without adequate study, the conclusions being drawn purely 

 on the basis of the fact that the amoebae were found in a host 

 from which they had not previously been recorded. This has been 

 done in spite of the fact that nearly every writer acknowledges 

 that he can see no morphological difference between his new species 

 and Endamocha coli of man. It is apparent that we must resort to 

 methods of differentiation more critical in character than a new 

 host environment alone if these names are to be justified. 



The same problem has also been encountered in respect to the 

 amoeba resembling E. histolytica of man, forms exhibiting similar 

 morphological characteristics having been found in several species 

 of monkeys, the rat, in the domestic pig and in naturally infected 

 kittens. The morphological appearance of these amoebae is identi- 

 cal ; they grow in L.E.S. culture medium; they produce similar 

 pathological symptoms in kittens experimentally infected ; and suf- 

 ficient animal transfer experiments have been accomplished to 



