jM. W. Jepps and C. Dobell 
357 
Blastocystis —which can, indeed, be found, if carefully sought, in most 
human beings—we have, we believe, in the present series one case (D. 4) 
which is uninfected with this organism. We do not, of course, deny that 
degenerate protozoa may be mistaken for Blastocystis] on the contrary, 
we believe that this is the key to the correct interpretation of Swellen- 
grebel’s observations. 
Although we have devoted much time to the search, we have never 
been able to discover any other stages of Dientamoeba than the free 
forms described above. No cysts, or stages resembling cysts, have ever 
been found. We thought at first that we should have no difficulty in 
discovering the cysts if we continued to examine the faeces of an infected 
case for a sufficiently long time. All our h^Des, however, have been 
disappointed. One case (D. 1) has now been examined 42 times during a 
period of ten months, and a most careful search for cysts has been made 
by both of us on very many occasions. Another case (D. 4) was examined 
with equal care 12 times in five weeks: but neither in the stools of these 
cases nor in those of any others infected with this amoeba have we 
succeeded in finding any structures which can be regarded as its cysts. 
When the stools of an infected person are soft or diarrhoeic—either 
naturally, or after the administration of a saline purge—the active 
amoeba can often be found in them: but when the stools are hard and 
formed no trace of its existence can be detected. In this respect 
Dientamoeba differs conspicuously from the other human intestinal 
amoebae^, and resembles the flagellate Trichomonas hominis. We, like 
other observers, have never succeeded in finding the cysts of this organism, 
in spite of the most diligent search. 
These two organisms— Dientamoeba and Trichomonas —differ remark¬ 
ably in this character from all the other intestinal protozoa of man. 
Both present, in consequence, the same difficulty in the way of under¬ 
standing their mode of transmission from host to host. It is possible, 
of course, that both form cysts or resistant bodies of some sort, and that 
these are formed very rarely or have been overlooked or mistaken for 
other structures. We find it difficult, however, to believe that these 
suppositions offer adequate explanations of the apparent invariable 
absence of cysts or cyst-like structures. It has been suggested by Wenyon 
1 Dientamoeba resembles, however, in this respect another amoebic inhabitant of the 
human body —Entamoeba gingivalis, the amoeba commonly found in the mouth. Although 
“cysts” of this organism have several times been found and described, we have found 
no good evidence that the structures so interpreted are really the cysts of the amoeba. 
We believe, accordingly, that its cysts—if it forms any—have still to be discovered. 
