THE SPECIES OF HUMAN AMCEB^ 167 



for the incidence of amoebic infections. All opportunities to make 

 surveys of infections of any native groups more or less isolated 

 from foreign contacts, should be seized upon and adequate mate- 

 rial in the form of permanent preparations secured and the species 

 determined with great care. 



The indications from available statistics of infection point to 

 the conclusion that these amoebic infections of man are age-old 

 and race-wide and have few if any geographical or racial limita- 

 tions. Confirming data are needed on this and especially from 

 primitive peoples in Australia and Africa, such as the negrito 

 stocks and the pygmies. It is possible that some significant varia- 

 tions in the incidence of infections by the different species of 

 amoeba may be found between the dififerent geographical regions 

 and dififerent racial stocks. In any event, marked differences in 

 the relative frequencies of infections, in the relative abundance of 

 individuals, and in the incidence of multiple infections may be 

 expected to be found in different ages, social groups, occupations, 

 races and regions, and correlations with sanitary conditions and 

 social customs will be brought to light by comparative surveys of 

 these parasitic infections. 



The ecological relations of these infections are but little known. 

 Nothing is known as to how far, if at all, the dift'erent chemical 

 elements of the diet, or particular types of food, favor, impede or 

 inhibit the growth of these amoebae en masse or differentially. The 

 relations of the other animal intestinal parasites, of previous 

 amoebic infections, of the sequence in the acquirement of infec- 

 tions, of reinfections, of the age at which they are acquired, of 

 the accompanying bacterial complex of the feces, or of the par- 

 ticular species of bacteria and yeasts, to the acquirement, persist- 

 ence, flare, or inhibition of the individual species of amoebae are 

 wholly unknown. Susceptibility of different individuals among cul- 

 ture animals should be tested, and the effect of varying numbers 

 of cysts in establishing infections in new hosts or increasing infec- 

 tions in old hosts should be tried out. Comparable tests with mate- 

 rial from cultures will be instructive. Changes in infectivity as a 

 result of culture should be investigated. 



Theories as to the phylogenetic relations of the amoebae of man 

 can be discussed only when a fuller knowledge of the amoebic in- 

 fections of the mammals as a whole are better known and when 

 host-parasite transfers have been studied more extensively, host 



