LABORATORY WORK IN DAIRY BACTERIOLOGY 2Q5 



growth color. Compare the growth with the different types 

 shown in figures 84 and 85, and determine with which each 

 agrees. Note the amount of elevation of the surface growth 

 and compare with figure 86. 



Bouillon. Note turbidity scum sediment. 



Fermentation tubes. See below (No. 30). 



Milk tubes. Note at 70 and 98 the development of acid as 

 shown to litmus paper curdling separation of whey appear- 

 ance of gas bubbles subsequent softening of the curd, called 

 digestion. 



Potato tubes. At 70 and 98. Note color of growth 

 abundance of growth texture of growth discoloration of 

 potato. 



By such characters as above determined, different kinds of 

 bacteria are distinguished and described. For a complete descrip- 

 tion more characters than those mentioned are necessary. The 

 characters of the cultures which have been named, Bact. lactis 

 acidi and Bact. aerogencs, should be compared with those given 

 on page 30 to see if they agree with the characters there given. 



*No. 30. Fermentation Tubes. Inoculate a series of fermen- 

 tation tubes (dextrose, lactose and saccharose) with different 

 bacteria. Among those chosen should be one culture of Ract. 

 lactis acidi, and one of Bact. aerogencs. In two days, note 

 whether gas has been produced in the closed arms, and, by 

 means of litmus paper, whether the bouillon has become acid. 

 If gas shows in the fermentation tubes, determine the gas ratio 

 as follows: 



Without disturbing the gas, fill up the bulb to the top with 

 a 2% NaOH. (By a mark, note the level of the gas in the glass 

 arm.) Place the thumb over the opening in such a way that 

 there will be no air bubble between the thumb and the surface 

 of the liquid. Now, invert the tube, allowing the gas to flow 

 out into the bulb, and, by turning back and forth, mix the gas 

 with the NaOH solution in the bulb, keeping the thumb very 



