46 BUTTER-MAKING. 
absence of air. These are called anaerobic. Some grow under 
either or both conditions, and are called facultative aerobic or 
facultative anaerobic. 
Temperature.—Favorable temperature is essential to bac- 
terial growth. Temperature is, indeed, the most important 
means by which the growth and development of bacteria can 
be controlled. The range of temperature at which bacterial 
growth can occur may be placed between freezing-point and 
ah 
tats 
ee LS SAIN ay t 
wf N vee 
We 0 GOA NS es 
rv Stee sy 
' aS t ‘ ~ vt 
vy TS i tae a i \ 
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TEs bee 
Fic. 7—a, single bacterium; b, progeny resulting from the growth of a bac- 
terium during 24 hours in milk at 50° F.; c, progeny of a bacterium 
during 24 hours growth in milk at 70° F. At 50° F. multiplication was 
5-fold. At 70° F. the multiplication was 750-fold. (Bul. 26, Storrs, Conn.) 
a little above 110° F. The growth of bacteria at these ex- 
treme temperatures is very slight. Even at 50° F. the rate 
of growth is very slow. According to experiments conducted 
by Dr. Conn, the multiplication of bacteria at 50° F. was 5- 
fold. while at 70° F. the multiplication was 750-fold. The 
following table shows the number of bacteria per cubic centi- 
meter in milk kept at different temperatures: * 
In 50 H No. of No. 
Bost | Bap | Hae | Hep | eu | eeebs.| metab 
set. o o o ‘urdli; 0! - 3] is 
Bt OOS abs 0". at BO". at 70°" Hite at 50° ling at 70°, 
46,000 | 39,000 | 249,500 |1,500,000 5 12,000,000 190 56 
47,000 | 44,800 | 360,000 | 127,500 | 792,000,000 289 36 
36 hours 
50,000 | 35,000 | 800,000 | 160,000 | 2,560,000,000 172 42 
42 hours 
* Bull. 26 Storr’s Stn., Conn. 
