HFFECT OF TEMPERATURE ON BACTERIA. 69 
at this temperature has, however, hardly been touched upon, 
although Schmidt and Neilson showed that five species which 
they had studied could grow at 0°. No observations have been 
made to determine what effect such low temperatures have in 
differentiating species in a medium containing at the outset 
many species of bacteria. It seemed desirable, therefore, to 
study this question in connection with the other experiments 
which have been carried on in our laboratory. 
The method of performing the experiments was essentially 
the same as previously described. A sample of milk was brought 
to the laboratory, plates made from it immediately, and then 
the sample divided into three lots. One lot was placed at the 
temperature of 1° above freezing, a second at 10°, and a third 
at 20°. ‘The three samples were then plated at varying inter- 
vals; the sample at 20° being plated every 6 hours, that at 10° 
every 24 hours, and that at 1°, for the first experiments, every 
2 days, but later the tests were made at intervals of 3 or 4 
days, and, in some experiments, not oftener than once a week. 
This change in the interval of analysis was made as a result of 
the study of the development of the bacteria in the early pre- 
liminary experiments. ‘The plates were incubated and carefully 
studied, and all kinds of distinguishable colonies were deter- 
mined. Samples of the colonies were isolated and subsequently 
carried through a series of cultures, for the determination of 
the characteristics of each species in question. ‘The results of 
these. determinations were to show that in most cases the 
species were those well known and already described, although 
a few of them appeared to be different. We found, in some of 
the experiments, that the species of bacteria which developed 
most abundantly at low temperatures were not those previously 
included in our lists. ‘The most interesting of these was No. 
259 of our list, which, as will be shown below, was'very persis- 
tent even at low temperatures. In the tabulation given below 
it was necessary to.change the method of arranging the figures, 
owing to the large number of species to be included. 
EXPERIMENT NO. 7. OCTOBER I0. 
The three samples of milk were treated as above described. 
The sample placed at 20° curdled in about 48 hours, and was 
‘strongly acid. ‘There was a large amount of gas present in the 
