i68 RESEARCH IN PROTOZOOLOGY 



specificity tested out more fully experimentally, and the border 

 lines of mere survival of transferred parasites are more accurately 

 determined. More must be knov^n of the possibilities of transfer 

 within new host species before much theorizing on phylogenetic 

 trees of human parasites will have value. 



It is especially desirable that our knowledge of amoebic infec- 

 tions in all of the primates be completed in order that some more 

 evidence may be secured as to how far down the simian line the 

 human infections may be traced. The distribution of the genera 

 of human amoebae in vertebrates as a whole is also of significance. 



The infections in all of the various domesticated animals with 

 which man has been associated in different parts of the world may 

 prove to be instructive and significant as to the phylogeny of some 

 of the human amoebae. 



The physiological problems awaiting investigation with human 

 amoebae are of necessity largely those accessible with amoebae in 

 culture, although certain problems are linked with the ecological 

 ones, and others require correlated studies in some culture mam- 

 mal. The metabolism of the various species in culture media should 

 be investigated with reference to the nature of the chemical sub- 

 stances utilized, the changing requirements at different periods 

 of the cycle, the effects of hydrogen-ion concentration and of oxy- 

 gen tension upon metabolism, upon the cycle, and upon the rate of 

 reproduction. The particular conditions which determine the loca- 

 tion of amoebae in restricted regions of the digestive tract, the 

 effects of the dift"erent digestive secretions upon the amoebae of 

 the different species, and the factors in the stool or in the blood 

 stream, or liver (if any), which favor encystment still await 

 determination. 



The effect of oxygen upon amoebae in both the motile and en- 

 cysted stages, in the intestine of culture mammals, and in culture 

 media should be tested. The critical temperatures, both high and 

 low, for each species in both the motile and the encysted stages 

 are as yet imperfectly known. 



The effects of the changes in the hydrogen-ion concentration 

 within the limits of toleration for both motile and encysted stages, 

 upon metabolism, and upon the shape and activity of the pseudo- 

 podia and the rate of movement invite investigation and a com- 

 parison among the different species both from stools and from 

 cultures. 



