520 Transactions of the Society. 



pseiidopodia in all directions (fig. 10). These capture the small 

 organisms, which may be seen passing towards the interior each in 

 a tiny vacuole, and when the amceba reassumes its bulky form the 

 endosarc appears to be a mass of small vacuoles. 



The nucleus is seen with difQculty in the living (figs. 9 and 

 10), especially when much food is present. It shows up clearly, 

 however, with such an intra-vitam stain as neutral red, and may 

 then be seen to be of the vesicular form and to some extent com- 

 pressible. There are generally a few granules of chromatin on its 

 memltrane. The small caryosome consists as a rule of a group of 

 granules (figs. 12, 13); occasionally these form a ring (fig. 11), as 

 is so often the case in Entamceha histolytica, which has a sliglitly 

 larger nucleus. In E. gingivalis the nucleus is generally only 

 3 or 4 /i in diameter, but may he 5 fi or even 6 fj, (fig. 11) ; possibly 

 these latter are about to divide, 



Eeproduction, so far as we know, only takes places by binary 

 fission, the nucleus dividing well in advance of the cytoplasm, so 

 that two nuclei in a specimen have been seen on several occasions ; 

 these may be of different sizes, e.g. 3 and 4 /x respectively (fig, 13). 

 Nuclear division is difficult to follow out in all its stages owing 

 to the deeply staining inclusions. These appear to persist during 

 the process, since two nuclei are found in amoebae with vacuoles 

 containing almost entirely digested food (fig. 13). If there be 

 any sexual process or cyst production in the life-history of this 

 amoeba in the mouth it must be very rare. The only cysts that 

 we have ever seen from the mouth have been obviously those of 

 some free-living amoeba of the Limax group (Vahlkampfia), i.e. 

 small (8-12 fi in diameter), with a nucleus containing a large 

 caryosome. The cysts described by Craig (S) from the mouth 

 appear to be the same. Drs. Penfold and Drew, working in London, 

 have recently cultivated an amceba from the mouth, but were 

 disappointed to find that it had a contractile vacuole, and was 

 obviously a free-living form and not E. yingivalis. That such cysts 

 frequently find their way into the mouth from uncooked vege- 

 tables, etc., is proved by the fact that they so often reappear in 

 the freces. 



All our attempts to grow E. gingivalis aerobically or anaerobically 

 on various media and in association with different bacteria have 

 been uns\iccessful. (It may be of interest to point out that no 

 parasitic amoeba has ever yet been grown artificially.) 



It is quite possible that there is more than one species of 

 amoeba in the mouth, but until some other stages in the life- 

 historv have been observed, inside or outside its host, it is 

 premature to try to divide them. 



It was in 1915 that Bass and Johns (1) produced, an elaborate 

 book in which they recorded the invariable presence of amoebae in 

 pyorrhoea lesions, and accused these Protozoa of being the specific 



