GENERAL roxsiDirKATiux OF I >i si-;asi;. 



59 



cf r,nconibined oxygen. ( )ther liacleria, facultative aei-ol)CS or 

 anaerol)es, are not so selecti^-e in their oxyo-en requirements, 

 e. g., some are capable of immediate ada])tation to a medium 

 containing free oxygen. It is ]irohai)le that anacrol)ic bacteria 

 recjuire oxygen as a res]iiratory gas but the oxygen is ol)tained 

 from oxygen compounds that are decomposed b^- these bacteria, 

 the ox}-gen probably being consumed while in the nascent state. 



^loisture, temperature and light arc other physical condi- 

 tions that affect bacterial develo]>mcnt. .\ xevv few bacteria 

 will remain active in substances containing less than t\\■ent^' 

 per cent of ^^•ater. The o]>timum condition relati\-e to moisture, 

 recpiires the presence of about Sii'/f of water. This fact is 

 obser^•ed in the preparation of dried food stuifs anrl is the 

 essential reason ^\div dessicants fa\'or wound healing or retard 

 infection. The temperature range of the various ])acteria is 

 wide. Some bacteria li\'e and thrive at a temperature near the 

 boiling point, others at a freezing temperature. Pathogenic bi'c- 

 teria, in general, require the temperature of their host. The 

 chicken has a ^•ery high normal temperature (loT" to liis° h'.), 

 and this mav explain its immunitv to practicallv all the diseases 

 that affect other domestic animals. All' bacteria require the 

 absence of light for their best de\'elc)pment. r>v ada]:)tation some 

 have become capable of growing and thri\-ing in da^dight. 



The effects of bacterial growth and the protlucts e\-ol\-ed 

 during bacterial growth vary according to the microorganism 

 in question and its environment. TTeat and light are two forms 

 of energv produced by bacterial activity. The heating obser\-ed 



