28 BACTERIOLOGY FOR NURSES 



and the bacflli of diphtheria and typhoid fever are 

 much less sensitive to low degrees of temperature 

 than to extremes of heat, sometimes surviving 

 weeks of freezing. A certain species of bacteria 

 commonly found in sewage shows no signs of growth 

 in a temperature below 60° C. (140° F.). The 

 iavor Me degreg ^oftemparature ,fQ£,-the^d evelQ p= 

 me ntof most p atliogenic_bacteria isJihat_Qf thejiu- 

 m^ibody^_37lQ.^.6° F.). 



The range between the minimum and maximum 

 degrees of temperature in bacterial resistance is 

 equally great, spores being much more resistant 

 than the vegetative forms; some spores withstand- 

 ing boiUng for sixteen hours, while the vegetative 

 forms are usually killed by ten minutes' exposure 

 to 60° C. (140° F.) with moisture. 



By J^;emaZ_jiga|A32iat is meant the degree of 

 temperature necessary to kill the organisms, in a 

 given time ; and as this varies with different species, 

 it is used as a means of identification, the thermal 

 death point of all of the common species being well 

 known. 



Light. — That light affects the activities of living 

 cells has long been known; the effects of Ught upon 

 the higher forms of life have been the subject of much 

 investigation during recent years. SunlighLjias a 



