KHFFECT OF TEMPERATURE ON BACTERIA. 4I 
Milk kept at 37°.—1. Although there was at first a notice- 
able development of the acid organisms, Groups I. and II. in 
the later hours Group III., 2. aerogenes, developed very much 
more rapidly. At the last test, just before curdling, Group 
III. had far outgrown all other species, and while Groups I. 
and II. were still quite numerous, the B. aerogenes had taken 
the lead, and constituted 68 per cent. | 
2. ‘The total numbers present at the time of curdling were 
very much less than in the samples kept at either 10° or 20°. 
HXPEHRIMENT NO. 2, FEBRUARY I3. 
This experiment was a repetition of the first, except that a 
larger number of plates were made at each test, of different 
dilutions, and the results, representing an average of several 
analyses, are more reliable than those of experiment 1. The 
milk was at a temperature of 7° when obtained (2 hours old). 
Plates were made of it at once, and samples placed at 12°, 20°, 
and 37°, and plated at intervals shown in the tables. The 
milk kept at 37° curdled in 18 hours, with a tough broken 
curd and much gas. That kept at 20° curdled in 56 hours. 
That kept at 12° curdled in 9% days. Analyses of the last 
were made up to the 196th hour. The details of the analyses 
are shown in Tables 4, 5, and 6. 
The three analyses of milk at 12°, taken at the end of 46, 
60, and 70 hours, show the results of too high a dilution, the 
number of colonies on a plate being only from Io to 30 in the 
different samples. It will be noticed that in these three plates 
only three of the different groups were detected. This was 
due to the fact that the dilution was so high that an average 
sample was not obtained, and the only species that appeared 
were those present in the largest numbers. ‘The three analy- 
ses, therefore, show us what types were present in the largest 
numbers, but do not give any evidence of those present in 
smaller numbers, and do not give us the proper analysis of the 
milk at these periods. 
. From the tables the following points are to be noted: 
Milk kept at r2°.—1. ‘There was a slight decline in total 
numbers until about the goth hour. 
4 
