KEI’OKT OF TRAVELLING PATHOLOGIST AND PKOTOZOOLOGIST 
12!) 
morphological appearances which were characteristic of these ammbaj and liy which they 
could be distinguished from one another. I found, however, that in healthy individuals the 
amoebsB might show features characteristic of Schaudinn’s dysentery amoeba, Entamaba 
histolytica, and, vice versa, in true dysenteries the amoebae might correspond completely with 
Schaudinn’s harmless Entammba coli. It is fortunate for us that there are other more definite 
means of distinguishing these amoebae. According to Schaudinn, Entanueba histolytica 
produces cysts, which are small, measuring only 3 to in diameter. These cysts have a 
tough membrane which obscures the contents. On the other hand, Entamceba coli produces 
cysts having a diameter of about 14p. The membrane enclosing them is clear and 
transparent, so that the contents are easily visible. It is quite evident that the differences 
between the cysts are such that they can be readily differentiated. However, I have been 
unable to discover the small cysts of Entanueba histolytica in any dysentery case I have 
examined. I have repeatedly found the cysts of Entamoeba coli in both dysentery cases and 
in healthy individuals. Schaudinn says that in only a small percentage of dysentery cases is 
Entamaba histolytica the exciting cause, so it is possible that I have not examined a case in 
which this amoeba is present. The presence of Entamceba coli in dysentery cases is only to 
be expected when it is known that it may also occur in healthy persons. Its presence is only 
accidental and has no bearing on the course of the disease. 
Schaudinn described in detail the life-history of Entamceba coli and the development of 
the cysts. I have shown elsewhere that the development of the amoeba living in the intestine 
of mice follows an almost identical course, so much so that it seems very probable that the 
amoeba of the mouse and that of man are identical, and possibly also the amoebifi of other 
animals. This opens up the question of domestic animals acting as alternative hosts for the 
amoeba found in the human intestine. 
I have not been able to trace every stage in the development of the cysts of Entamoeba 
coli from man ; but I have seen a sufficient number of different stages, and these correspond 
so closely with Schaudinn’s description and my own findings in the case of the amoeba of mice 
that there can be little doubt that the development described by Schaudinn is the correct one. 
In this development an amoeba becomes freed of all food particles, which are thrown out 
from the body, and then contracts to a spherical shape. Around this spherical mass of 
protoplasm, which contains a single nucleus, there forms a thick gelatinous covering which 
quickly contracts to a tough transparent envelope. The single nucleus divides into two, 
and within the tough envelope there forms a thin membranous second covering to the 
encysted amoeba. There are now two nuclei situated at opposite poles of the cyst. Each 
nucleus now divides twice to give off two reduction bodies, which degenerate. The two 
remaining nuclei, which are now smaller and poorer in chromatin, divide again, so that there 
are two pairs of nuclei lying at opposite poles of the cyst. One nucleus in each pair begins 
to move away from the other, which remains stationary. The moving nucleus of each pair 
crosses over to the opposite side, where it comes in contact with the stationary nucleus, 
finally fusing with it. In this way there is brought about an interchange of nuclear material 
between the two nuclei. After conjugation a stage with two nuclei is again reached. 
Each of these nuclei divides to produce a cyst with four nuclei, and each of these four to 
give eight nuclei. 
At this stage there is a cyst containing a single mass of protoplasm in which are embedded 
eight small nuclei. No further development takes place till after the cyst has escaped from 
the body. These cysts can withstand drying, and could be carried about by wind and water. 
When taken into the intestine of a new host the mass of protoplasm within the cyst divides 
into eight small amccbiE, which escape hy the rupture of the cyst and so infect the new host. 
In the human intestine it is common to meet with cysts containing two, four, or eight 
Work on 
/i. histolytica 
li. coli 
Stages in the 
development 
of E. coli 
I 
