CHAPTER IX. 



INFLUENCE OF TEMPERATURE AND LIGHT ON 

 BACTERIA. 



TEMPERATURE influences life phenomena in two ways chemi- 

 cally and physically. Chemically, heat influences powerfully the 

 reacting velocity within the cell and the aggregate condition of the 

 molecules, or coagulation. Physically, temperature influences the 

 viscosity of the liquids composing the cell. 



Temperature and Speed of Reaction. According to the law of 

 Van't Hoff and Arrhenius, a chemical reaction is increased two or 

 more times its original speed whenever the temperature is increased 

 10 C. This holds good for the reactions in living organisms, within 

 certain limits of temperature, as well as for non-living, as may be 

 seen from the following table given by Clausen in which is recorded 

 the number of milligrams of carbon dioxid produced by 100 grams 

 of lupine seeds in one hour : 



Carbon dioxid Increase 



Temperature. produced. lor 10 r C. 



7.27 



5 13.87 



10 18.11 10.84 



15 34.37 



20 43.55 25.44 



25 58.76 



30 85.00 41.45 

 35 . 100.00 



40 115.90 30.90 



45 104.45 



50 46.20 69.70 



55 17.70 



The above table shows that for temperatures below 40 C. there 

 is a general increase in the speed of the reactions with increases in 

 temperature. However, at higher temperatures the amount of 

 carbon dioxid diminishes rapidly with further increase in tempera- 

 ture. This is very generally observed in enzymatic processes, as at 

 temperatures over 60 C. enzymes are rapidly decomposed and 

 many become immediately inactive when they are heated up to 

 63 to 65 C. This may be due to the fact that the enzymes them- 

 selves undergo hydrolysis which also would follow the temperature 

 law of Van't Hoff and Arrhenius. Furthermore, enzymes are prob- 

 ably protein and would undergo heat coagulation. This would 

 reduce the reacting areas between enzymes and fermentable sub- 



