55 



ance of the gas is H. (There are also traces of other gases) . 

 Its explosive property can be tested by filling the open bulb 

 with water, cover it with the thumb and again bring the gas 

 to the open bulb, hold it close to a flame and remove the 

 thumb. A distinct explosion will be heard. 



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

 urements. Thus the total amount of gas = 5 cm. The 

 amount absorbed (CO 2 ) = 2 cm. The remaining gas or 

 3 cm. = the H. The ratio of CO 2 to H is, therefore, as 2:3 

 or CO 2 :H: 12:3. 



EXERCISE XXIII. 



IDENTIFYING GENERA OF BACTERIA AND OBTAINING 

 PURE CULTURES FROM COLONIES. 



86. General directions. Examine the bouillon cult- 

 ures made from the impure or mixed culture in both the 

 fresh condition and in stained cover-glass preparations. 

 Stain with carbol fuchsin and an aqueous solution of methyl- 

 violet. Describe the appearance of the bacteria in these 

 preparations and note the number of genera present. Give 

 the names of the genera and note the one which predomin- 

 ates in numbers. 



Examine and carefully describe the colonies on the plate 

 cultures. Determine the number of different colonies, and 

 carefully describe each. 



Inoculate a tube of bouillon from a colony from each genus. 

 Label the inoculated tube with the name of the genus. Make 

 stained cover-glass preparations from a colony of each genus 

 Mount and label one of these preparations to accompany the 

 notes. 



