142 



lodamcebe butschlii (Fig. 39) is a small ameba (usually 9 n to 

 13 JJL in length) the characteristics of which have been sufficiently 

 described on p. 132. The cysts of this species (Fig. 39B) were 

 until recently thought to be of vegetable nature and were known 

 as Iodine or I. cysts. The cysts are not smaller than the free 

 amebae; they are of very irregular shape, as if formed under 

 pressure. This ameba, also, has a wide geographic distribution 

 and, while not so common as the intestinal amebae hitherto dis- 

 cussed, the available data indicate its occurrence in from 3 per 

 cent to 5 per cent of all human beings in temperate or tropical 

 climates. 



Another very small human ameba, Dientamoeba fragilis (Fig. 

 40), has recently been described by Jepps and Dobell. This 

 species averages only about 8 or 9 /z (^-fa-$ of an inch) in diameter, 

 thus resembling Endolimax nana. The free amebae are active, 

 showing well marked ectoplasm and endoplasm. The pseudo- 

 podia are of ectoplasm, and are flat and leaf like (Fig. 40B). The 

 peculiar features of the organism are described on p. 129. The 

 most characteristic feature of this ameba is the division of the 

 nucleus shortly after cell division has occurred, so that mature 

 individuals have two similar nuclei. No cysts have yet been 

 found, yet it is highly improbable that the infection is transmit- 

 ted by the free amebse, since the latter are very short-lived outside 

 the body. The habits of the organisms are probably similar to 

 those of the harmless amebae already described. Only ten cases 

 of infection have so far been discovered, but the evidence afforded 

 by these cases indicates a wide geographic distribution. 



Mouth Amebae 



The occurrence of amebae in the human mouth has been known 

 for many years, but particular interest has attached to them 

 only recently, since a number of investigators have brought forth 

 evidence to show that the common mouth ameba, Endamoeba 

 gingivalis, is pathogenic, and an important factor in pyorrhea. 



Pyorrhea, or Rigg's Disease, in some stage afflicts the ma- 

 jority of all adult people, and over 50 per cent of all permanent 

 teeth which are lost are lost as the result of pyorrhea. The 

 apparent relation between this disease and the presence in the 

 mouth of the above-mentioned ameba, E. gingivalis (or buccalis), 

 was first demonstrated in 1914 by Smith and Barrett. Since 



