FA\"(>kAi;iJ': C()Xi)iTi()Xb mjr bactkkial (.rowjii 57 



range. Some few species will lthw at as hi,Lrh a lernperatiire as 

 140'" F., and B. hulgayiciis will irrow vcr\- rapidl}- at i 10 ]•'. 



The growth of bacteria at these extreme tenijierature.^ ib 

 usually very slight. Even at 50'' V. the rate of growth i., wry 

 slow. According to e.\i)erirrients conducted lj_\- I.)r. Conn, the 

 multiplication of bacteria at 50' V . was 5-fold, while at yo' F. 

 the nniltiplication was 750-fold. The following table show^ the 

 number of bacteria per cubic centimeter in milk kept at different 

 temperatures.^ 



All bacteria do not ha\'e the same optimum growing tem- 

 perature. Some species de\x-lop most rapidly at one tempera- 

 ture, while other species prefer a difl'erent temperature for the 

 greatest development. It is on this account that certain tem- 

 peratures are employed in ripening starters and cream. Accord- 

 ing to researches by Conn, Baclcriuiii acroi;ciics de\x-]ops Ax-ry 

 rapidly in milk at 95° F. This particular species, producing 

 much gas and an unpleasant flaA-or, sours milk Ax-ry ra[)idly. As 

 a rule, milk which has been held at this high temjoerature con- 

 tains a preponderance of this undesirtdde si)ecies of bacteria. 

 At 77^ F. results are more uncertain; the species of bacteria 

 which will i)redominate in milk at this temperature depends in 

 large measure upcjn the nutnber of each kind originalh- present. 

 According to Conn Streptococcus lacticus has the highest relatiAx- 

 growth at about 70^ F. This particular species produces no gas, 

 and its presence is desirable in cream for butter-nxiking. ]\Iilk 



' Bull, 26 Storr's Sta., C..>nn. 



