EFFECT OF TEMPERATURE ON BACTERIA. 79 
Group IV., as well as the large number of liquefying bacteria, 
which produced an alkaline reaction, neutralized the acid de- 
veloped to such an extent that no curdling took place. At the 
close of the experiment the acid bacteria had come to be nearly 
as abundant as those of Group IV., but even at this time no 
curdling took place. 
5. The liquefying bacteria continued to develop constantly 
during the whole experiment, and were present in large 
numbers at the end—about ro per cent. 
Milk kept at ro°.—1. Here the species No. 249, above 
referred to, produced a modification even greater than at 1°. 
Table 23 shows that Group IV. contained two species, No. 
194, which was abundant in the early experiments, and No. 
249, Which was abundant in the later experiments. Inasmuch, 
however, as these two species were not readily distinguishable 
on the plates, it was impossible to separate their colonies and 
determine their proportions in successive tests; nor was it pos- 
sible to state when No. 249 began to develop at the expense 
of No. 194. 
2. After the 96th hour the species No. 249 began to develop 
with a rapidity never before seen by us in any experiment, so 
that the numbers grew phenomenally high. The plates made 
from this time up to 336 hours showed such very high numbers 
that differentiation of species was absolutely impossible, and 
though an attempt was made to procure such differentiation, 
the results are too unreliable for tabulation. The numbers of 
bacteria in the plates indicated that the milk contained, at about 
300 hours, as many as 200,000,000,000 per cubic centimeter, 
the number having risen regularly, in successive hours, to this 
point. After this time the number dropped back again. The 
final tests, made at 336 and 408 hours, were once more within 
the reach of our experimental methods; a differentiation of the 
species was possible, and it is given in the last two columns of 
the table. ‘These two columns show that, at this time, 24 per 
cent. and 41 per cent. respectively of the bacteria were of the 
species No. 249, but that the bacteria of Group I. had now 
become more abundant than Group IV. ‘The liquefiers also 
became quite abundant at the end. 
