10 General Bacteriology. 



N. B. Some time is required to raise the temperature of the media to that of the steam, 

 especially if the vessels are large. 



All media should be carefully examined every day for a week or more, and if "specks" 

 or the least cloudiness appears, the medium is not sterile and the process of sterilization 

 must be repeated. 



All receptacles containing media should be labeled after sterilization. For this pur- 

 pose labels can be purchased, the size used for glass slides, or gummed paper in sheets 

 can be cut into squares (2 cm.). The labels are to be attached to each vessel 1 cm. from 

 the lip. The kind of medium and the date of preparation should be written across the 

 top, as io"is- L> 99 leaving the rest of the label to be filled in when the medium is inoc- 

 ulated. 



EXERCISE VII. PREPARATION OF GELATIN. 



GENERAL DIRECTIONS. 



a to d. Same as bouillon. (IV.) 



e. Add 1% peptone; 0.5% salt and 10-15% * of best white gelatin, and weigh. 



/. Heat until ingredients are dissolved. 



g. Neutralize. 



h. Boil 5 minutes and restore weight. 



i. Test reaction. 



j. If neutralized by method A add 5 cc. of a normal hydro- 

 chloric acid. In method B omit acid. 



k. Cool and add egg and boil 5 minutes. 



I. Filter. Arrange the apparatus shown in fig. 3. Use 

 absorbent cotton. The funnel and flask should first be heated 

 with warm water. Start the filter pump before pouring in the 

 culture medium. This prevents the unfiltered gelatin from TiTsTT^aratus for filtering 



passing between the COtton and the glass. media through absorbent cotton; 



"' layer of cotton : * tubes for 



Tnhp (V } 

 "* J making connection with air 



W. Sterilize. pump; c t Bunsen valve to prevent 



-r , i entrance of water into flasks. 



o. Label. 



REFERENCES. A. 95; H. 42; M. & R. 46; McF. 127; N. 153; P. B. C. 26. 



SPECIAL DIRECTIONS. Make 1 liter, using method A. Fill 30 test-tubes. Put 

 the remainder in flasks, sterilize in steam sterilizer or autoclave. Remember long exposure 

 to high heat injures the solidifying properties of gelatin. 



EXERCISE VIII. PREPARATION OF AQAR. 



GENERAL DIRECTIONS. 



a. Add 15 grams of agar-agar threads (finely chopped) to 500 cc. of water and either 

 (l)boil until the agar-agar is dissolved (about^hour) and make up loss of water by evap- 

 oration, or (2) dissolve in autoclave by heatingup to 120 C., closing off gas and allow- 

 ing to cool. 



* The amount to be varied according to the season of the year, 10 per cent in winter, 12-15 per 

 cent in summer, but it should be remembered that different quantities affect the appearance of the 

 culture. 



