20 PHYSIOLOGY OF BACTERIA 



experiments by Berghaus (1907) showing how different 

 organisms can resist different oxygen concentrations to 

 which they had been exposed for twenty-four hours. 



Many years later, Callow (1924) measured quanti- 

 tatively the amounts of oxygen taken up by washed 

 living bacteria suspended in buffer solution. The 

 amounts varied from 5 to 25 c.c. of oxygen (7-35 mg). 

 per gram of bacteria solids per hour, and remained con- 

 stant for many hours. Even after drying in vacuo and 

 re-suspending, three species took up as much oxygen as 

 before, while Ps. pyocyanea used very much less oxygen. 

 The experiments included 



Ps. pyocyanea, Ps. fluorescens 



Bad. prodigiosum, alkaligenes, coli, proteus 



B. megatherium, suhtilis 



Micr. pyogenes aureus, Sar. aurantiaca 



Mycohact. phlei 

 The experiments were also extended to Strept. lactis and 

 Clostr. sporogenes; these took up less than 0.5 c.c. during 

 the first hour, and practically none thereafter. This 

 seems to contradict the fact that these organisms are 

 very sensitive to oxygen. An explanation will be tried 

 on p. 74. 



(e) SUMMARY OF FACTS 



Yeasts and bacteria if left in moist condition without 

 food for a number of days will lose nitrogenous com- 

 pounds, which can be found in the liquid surrounding 

 them. The same process takes place if the organisms 

 are given carbohydrates, but no nitrogenous food. The 

 decrease of nitrogenous material in the yeast cell is 

 accompanied by a decrease in its fermenting power. 

 Ultimately, the cells die. Nitrobacter loses very 

 promptly part of its power to oxidize if carbon dioxide is 



