CH. Xl] BACTERIA IN THE SEA 271 



case with all forms of bacterial action. The investigation of 

 the relation of temperature to rapidity of denitrification is of 

 the very greatest importance from our point of view. In a series 

 of observations on this point Baur obtained the following results : 

 For Bacterium actinopelte in mixed culture. 



(1) Temperature 25° C. Denitrification began about 24 hours 

 after inoculation and lasted for a period of time varying from 7 

 to 11 days. At the end of this time combined nitrogen had dis- 

 appeared from the solution. 



(2) Temperature 15" C. Denitrification began about 4 days 

 after inoculation and lasted for about 27 days after which the 

 solution was nitrite-free. 



(3) Temperature 4° — 5° C. Denitrification began after about 

 20 days and after 112 days the reaction was still incomplete, that 

 is the tubes still frothed shewing that nitrogen was still being 

 evolved. 



(4) Temperature 0° C. During a period of 107 days there 

 were no signs of denitrification. 



For Bacterium lohatum in mixed culture. 



This bacillus gave very similar results. It was however able to 

 denitrify at a temperature of 0° C. but the amount of nitrogen 

 evolved was extremely small. 



The investigation of pure cultures of both species gave results 

 very similar to those obtained for mixed cultures. 



Thus the activity of the denitrifying bacteria investigated so 

 far depends on the temperature. It is greatest at about 25° C. and 

 it practically ceases at the temperature of freezing water. 



Now the reactions of bacteria are of the very greatest signifi- 

 cance in the circulation of carbon and nitrogen in nature. 

 Resuming very briefly the statements of this chapter we find that 

 there are in the sea : 



(1) The ordinary putrefactive bacteria which break down 

 dead proteid matter with the result that the nitrogen of the latter 

 is finally dissipated in the form of ammonia. 



(2) The ordinary fermentative bacteria which break down 

 carbohydrates and fats, with the result that the carbon of the latter 

 is dissipated in the form of carbon dioxide, and the hydrogen in 

 the form of water. 



