EFFECT OF TEMPERATURE ON BACTERIA. ah 
THER EFFECT OF DIFFERENT TEMPERATURES IN 
DETERMINING THE SPECIES OF BACTERIA 
WHICH GROW IN MILK. 
BY H.W. CONN AND W. M. ESTEN. 
[Acknowledgment is hereby made to the Rockefeller Institute for assistance in 
carrying out the experiments here described. } 
For the last three years work has been done in this laboratory 
upon the relation of the growth of bacteria in milk to a variety 
of conditions. Several previous reports of this work have been 
published in the last two years (Ann. Rep. of Storrs Sta. 1901, 
Uo een ee wevontacim avs lait) vol. sl. 1o01,-vol: IL 61903 js 
The most important conclusions reached in the work hitherto 
reported have been: 1. At the temperature of 20° C. the com- 
mon Bacterium acidi lactis grows with especial rapidity, and 
seems to be more favored by this temperature than is any 
other species. 2. At 13°C. the ordinary acid organisms do not 
grow so readily as at 20°C., but other species of bacteria do 
develop readily. 3. The percentage of acid bacteria increases 
with the total number of bacteria in ordinary market milk, 
provided that milk is kept at moderately warm temperatures. 
From the last fact it has been suggested that by a qualita- 
tive analysis, which will detect the percentage of the ordinary 
lactic bacteria, it is possible to determine whether a sample of 
market milk that contains large numbers of bacteria is old and 
has been kept at a low temperature, or whether it is fresher 
‘ but has been kept at a higher temperature. Experiments 
upon the effect of temperature upon bacterial growth have been 
extended and carried on in more detail and with greater care 
during the last year. The purpose of these experimeuts, re- 
ported in this paper, has been: 1, to extend the observations 
of the effect of temperature upon the species of bacteria which 
grow in milk, so as to include a wider range of temperatures; 
2, to determine whether there is any regularity in the results. 
A 
