28 STORRS AGRICULTURAL EXPERIMENT STATION. 
The significance of the questions thus studied is considerable. 
Their bearing upon the hygienic problems of milk will be recog- 
nized when it is remembered that normal lactic bacteria -are 
quite harmless to health, and that the troubles attributed to milk 
bacteria must be associated with other species. The develop- 
ment of lactic bacteria has been shown to check the growth of 
other species. Hence it follows that conditions favoring the 
growth of lactic bacteria may actually make the milk more, 
rather than less, wholesome; while conditions that check their 
growth may favor the development of other more harmful bac- 
teria, and, while preserving the milk from souring, actually 
render it less wholesome. It has actually been suggested by 
Bernstein (Milchztg., 1904, p. 133) that the most healthful 
method of treating milk for public consumption is to destroy 
its bacteria by pasteurization and then to inoculate it witha 
heavy culture of lactic bacteria. The ordinary method of pre- 
serving milk is by the use of low temperatures, and it becomes 
needful, therefore, to learn exactly what effect the low tem- 
peratures have upon the milk bacteria, not upon numbers sim- 
ply, but upon species. 
The bearing of these facts upon dairy problems is no less 
close. It is known that certain dairy species are useful to the 
butter maker and necessary to the cheese maker, while others 
are deleterious. Some species ruin the taste of butter, and 
«¢ 
others fill cheese with gas, producing the ‘‘ gassy curd’’ and 
‘“swelled cheese’’ which the cheese maker so much dreads. 
To check the growth of these species and to favor the growth 
of the desired types is the object of controlling dairy conditions. - 
The close relation of these problems to temperature makes it 
especially desirable to know what effect variation in tempera- 
ture has upon the growth of different types of bacteria. It is 
for the purpose of obtaining light upon the two problems, the 
one of the dairy and the other of public hygiene, that the long 
series of experiments outlined in this paper were undertaken: 
and the importance of the problems gives value to the results, 
even though, for reasons to be explained, the results can as yet 
be regarded as only approximately accurate. 
