120 
W. GLEN LISTON AND 0. H. MARTIN. 
A number of sterile agar plates were smeared with fresh 
sterile guinea-pig’s liver. These were placed in the incubator 
for two days to make sure that no bacteria had been planted 
on the surface of the medium during the preparation of the 
plates. Then to plate (a) a drop or two of an emulsion 
of the yellow coccus in saline solution, which had been boiled, 
was added at the same time as some bacteria-free cysts were 
planted on the liver-smeared culture. To (b) a drop or two 
of sterile saline solution was added as well as a few 
bacteria-free cysts. To (c) a drop or two of very weak sterile 
sodium carbonate solution with bacteria-free cysts was added. 
To (d) a few living yellow cocci in salt-solution were added 
with bacteria-free amoeba- cysts. 
The plates were then placed in the incubator and on the 
following day were examined. In each case living and 
moving amoebae were observed. The plates were kept under 
observation for some days longer, and it was noted that while 
very little multiplication of the amoebae had occurred in 
cultures A, b, and c in D, in the neighbourhood of the colonies 
of cocci, the amoebae had multiplied enormously. 
So far as it is possible to judge from a single experiment 
like the above, it would appear that multiplication of the 
amoebae only occurs in the presence of some substance which 
is apparently connected with the life of the bacteria, a 
substance which is destroyed by boiling. In this connection 
the following casual observations are worthy of record : On a 
number of occasions it was noticed that if the number of 
cocci planted with the amoeba-cysts was considerably in 
excess of the number of cysts, and particularly if the medium 
in which the culture was made favoured the development of 
the cocci, the amoebae failed to develop, while the cocci 
flourished. On two or three occasions, when apparently a 
culture of amoebae was growing well and multiplying in the 
presence of a colony of the yellow coccus, a stage was reached 
when the bacteria appeared to have produced some secretion 
which, diffusing outwards from the colony, caused those 
amoebae which were in the immediate neighbourhood of the 
