224 LORANDE LOSS WOODRUFF 
optimum conditions of light and temperature, are so adjusted that 
for a considerable period a practically self-supporting and self-suf- 
ficient microcosm exists—but with the balance of nature estab- 
lished neither the Protozoa nor bacteria can ever again attain their 
maximum abundance. 
C. THE 4A, B AND C GROUPS OF INFUSIONS 
All three types of infusions (A,B,C) which were made up gave 
the same general cycle of events, but the A and C’ series were 
shghtly slower in development (as one would expect from the 
presence of the hay) than the B series. The cycle of the C series 
was essentially the same as that of the A series except that it pro- 
gressed somewhat more slowly until the hay became thoroughly 
soaked. A practical disadvantage of the C’ series is presented by 
the fact that the unboiled hay, containing considerable air, has 
a tendency to float and so changes somewhat the distribution of 
the organisms until it sinks to the bottom at about the end of two 
weeks. This nuisance may be avoided by weighting the hay with 
glass. So far as length of cycle is concerned, however, both the 
A and the C series offered equal advantages for study, but the 
eycle of the B series (without hay) being considerably shorter, 
the sequence of the different types of organisms was more rapid, 
the number of organisms present was much smaller, and stable 
equilibrium of the infusions was attained sooner (ef. figs. 5, 6, 7). 
However, since the richness of the animal life was seriously de- 
creased, this series did not prove to be the best for study, and 
accordingly such a method of making up cultures is not recom- 
mended for investigations of this character. Nevertheless, the 
results derived from all three types of cultures will be given here. 
The data from each of the twenty-six cultures have been re- 
corded (as already described), then these data from each culture 
of each set of experiments of the A, B, and C series, started at the 
same time, have been averaged together. Therefore, in discuss- 
ing these data, I shall refer (unless it is specifically noted to the 
contrary) to the average number of organisms, time of appearance, 
ete., in infusions comprising each group as follows: 
