118 MICROBIOLOGY 



(There are also traces of other gases.) Its explosive property 

 can be tested by filling the open bulb with water, covering it 

 with the thumb and again bringing the gas to the open bulb, 

 holding it close to a flame, and removing the thumb. A dis- 

 tinct explosion will be heard. 



The ratio of C0 2 to H can be determined from the meas- 

 urements. Thus if the total amount of gas in the closed 

 branch = 5 cm., and the amount absorbed (C0 2 ) = 2 cm.,, 

 the remaining gas, or 3 cm., = H. The ratio of CO 2 to H is, 

 therefore, as 2 : 3, or C0 2 : H : : 2 : 3. 



2. To determine the effect of the bacteria on the me- 

 dium. 



(a) Fermentation of sugars producing acid with or 

 without gas. The gas consists largely of C0 2 and H. More 

 C0 2 is formed when alcohol is produced. C 6 H 12 6 (Glucose) 

 plus bacteria equal 2C 2 H 6 (Alcohol) plus 2C0 2 . 



More H is formed when butyric acid is produced. 



C 6 H 12 6 plus bacteria equal C 4 H 8 2 (Butyric acid) plus 

 2C0 2 plus 2H 2 . 



No gas is formed when lactic acid is produced. 



C 6 H 12 6 plus bacteria equal 2C 3 H 6 3 (Lactic acid)* 



When acid is produced in milk casein is coagulated. In 

 fermentation of the nitrogenous bodies alkalies are produced, 

 as CO(NH 2 ) 2 (Urea) plus H 2 plus bacteria equal C0 2 plus 

 2NH 3 . 



When alkalies are produced fats are saponified. 



(b) Peptonizing. This is manifested in the liquefaction 

 of gelatin or blood serum. 



In the examination of cultures they should be carefully 

 observed from day to day for the purpose of noting any 

 changes that may take place. Usually they are fully de- 

 veloped and the changes completed within a few days. It 

 is of the greatest importance that the changes in the cultural 

 characters and manifestations of the different species be 

 carefully determined, for it is by these changes that the 

 different species and varieties of bacteria are determined. 

 As bacteria lose certain of their properties, such as the power 



