138 



PRODUCTS OF VITAL ACTIVITY. 



formed by oxidation of the alcohol, producing from it carbon diox- 

 ide and water. 



The formation of acetic acid from alcohol is shown by the follow- 

 ing formula : Ethyl alcohol CH 3 .CH 2 .OH + O 2 = CH 3 .COOH + H a O. 



Butyric acid is produced by a considerable number of bacteria, 

 one of which, named Bacillus butyricus, has received the special at- 

 tention of Prazmowski. This is strictly anaerobic. In solutions of 

 starch, dextrin, sugar, or salts of lactic acid, when oxygen is ex- 

 cluded it produces butyric acid in considerable quantity, and at the 

 same time carbon dioxide and hydrogen gas are set free. Duclaux 

 gives the f ollowing formula of a solution containing lactate of lime 

 in which the action of the butyric-acid ferment may be well studied : 



Water, 



Lactate of lime (pure), 

 Phosphate of ammonia, 

 Phosphate of potash,. 

 Sulphate of magnesa, 

 Sulphate of ammonia, 



8 to 10 litres. 



225 grammes. 



0.75 



0.4 



0.4 



0.2 



FIG. 77. 



This is introduced into a flask with two necks, such as is shown 

 in Fig. 77. Having filled the flask with the culture liquid, the bent 

 neck is dipped into a porcelain dish containing the same. Heat is 

 then applied both to flask and dish, and the liquid in each is kept in 

 ebullition for half an hour. By this means the air is completely 

 driven out of the flask. This is now allowed to cool, while the fluid 

 in the shallow dish is kept hot, so that the liquid mounting from it 

 into the flask shall be free from air. When the flask is full it is 

 transferred to an incubating oven heated to 25 to 30 C., and the bent 

 tube is immersed in a dish containing mercury. The little funnel 



