174 LABORATORY GUIDE IN BACTERIOLOGY 



inside surface of the flask is covered with two coats. 

 For large sacs three coats should be applied. When 

 the celloidin is nearly dry water should be run into 

 the flask until filled. This water should be changed 

 several times. Commencing at the top of the flask 

 the film is separated from the glass and by means of a 

 smooth instrument, for instance, a glass rod which 

 has been rounded off at the end, the film is slowly 

 removed from the glass. As soon as there is a fairly 

 large part of the film separated, the water may be 

 emptied out and water run in between the film and the 

 glass. In this manner the film is gradually removed 

 from the glass. If the celloidin is too dry before the 

 flask is filled with water, it will crack and will be 

 difficult to remove from the glass. The technic is not 

 difficult and with some practice and care sacs can be 

 made which will be large enough to hold two liters of 

 liquid. 



SECTION s 



THE FORMATION OF NITRATES FROM NITRITES, 

 AND ISOLATION OF NITRATE BACTERIA 



EXERCISE I. THE FORMATION OF NITRATES FROM 

 NITRITES 



1. Prepare a solution as described on p. 39. 



2. Prepare a series of five flasks and place 50 c.c. of 

 the solution in each. 



3. Sterilize in the autoclave. 



4. Inoculate the first flask with soil and incubate at 

 room temperature. 



5. As soon as growth has appeared inoculate a 

 second flask, from this one a third, etc., as in Exercise 1, 



