D. Ward Cutler 
131 
Control 
Tyrosin 0-2 % 
„ 0-5 
„ 001 
No. of amoebae 
at start 
15 
13 
18 
16 
No. of amoebae 
present after 
12 hrs incub. 
18 
21 
24 
18 
Skatol. This substance in the strength of 0-5 % rapidly induced cyst 
formation, practically every one of the amoebae becoming encysted: a few, 
however, died as a result of the experiment. These results were obtained in 
every one of the twelve experiments performed and in each experiment six con¬ 
trol cultures containing no skatol were used. It is of interest in this connection 
to note that all the encysted amoebae possessed a nucleus typical of encysted 
amoebaefrom dysenteric stools (nucleus not of “ histolytica ” type). As amoebae 
with all types of nuclei occur in cultures, it appears possible that the forms 
killed by skatol had nuclei of the “histolytica’’ type. This seems likely 
because, in preparations stained with methyl green, the amoebae, which had 
not encysted, and appeared to be moribund, had nuclei very poor in chro¬ 
matin and of “histolytica” type. 
The significance of these observations will be more clearly seen by refer¬ 
ence to page 141. 
The influence of skatol in inducing cyst formation is of interest because 
this substance occurs naturally in the large intestine: as does also tyrosin, as 
a result of autolysis. 
It is well known that in dysentery infections, at the base of the ulcers, 
there occur large tissue-invading forms of E. histolytica ; while at the surface 
of the intestinal mucosa the “minuta” cyst-forming stage is frequently 
encountered. It is possible that the presence of skatol in the gut lumen may 
induce cyst formation, but it cannot be the sole cause, since in the cat’s gut 
cyst formation probably never occurs, although skatol is present. 
The Trophozoite. 
APPEARANCE OF THE LIVING AMOEBA. 
As previously stated, E. minuta represents the precystic stage of E. 
histolytica. This stage is dealt with under cyst formation (see p. 135). 
The endoplasm of all stages is often granular in appearance, and stains 
a bright pink with a weak solution of neutral red. Forms, especially in cat 
infections, are very commonly found with a distinctly alveolated endoplasm, 
Plate VII, figs. 1, 2, the alveoli are irregular as regards size and are not evenly 
distributed. The endoplasm is distinctly marked off from the ectoplasm, and 
when neutral red is employed this demarcation is very apparent as the 
ectoplasm remains unstained. Numerous food particles are usually found in 
the endoplasm: the most common being red blood corpuscles, which are 
sometimes present in large numbers, fig. 3. Leucocytes and bacteria are also 
ingested. 
