MILK FERMENTATIONS 



73 



More exact results can be obtained by the use of special 

 anaerobic culture methods (see p. 82). 



Exercise. Note the presence or absence of growth in the closed 

 and open arms of the fermentation tubes inoculated with various 

 cultures (p. 70). 



ABC 

 FIG. 14. TYPES OF GROWTH IN FERMENTATION TITBES 



A, facultative anaerobic organism ; H, aerobic organism ; 6', gas formation by 

 facultative anaerobic organism. (After Smith) 



Relation to temperature. The relation of the developing 

 organism to temperature is determined by noting the com- 

 parative rapidity of growth at 20 C. and at 37 C. Every 

 organism has a more or less definite temperature range from 

 the minimum to the optimum, and finally to the maximum, 

 temperature at which growth will go on. Generally most 

 bacteria prefer a relatively high temperature, such as blood 

 heat, but some of the fermentative types find ordinary air 

 temperatures almost as suitable as the higher degree of heat. 



The ability of the organism to resist the temperature of 

 80 C. for fifteen minutes should be determined, since it gives 



