75 



Prepare like the gelatin medium. Titrate to -f-i.o per cent. 

 Agar is difficult to filter, and the medium is never quite clear. The 

 agar medium liquefies at a higher temperature than gelatin, and does not 

 tend to remain liquid, no matter how often or how long it may be 

 heated. 



J. A gar-gelatin Medium. This has the advantage of both media, and 

 is now much used in general bacteriological work. 



Agar, 8 gm. , 



Gelatin, 40 gm. 



Salt, 5 gm. 



Peptone, 10 gm. 



Distilled Water, 1000 cc. 



Mix, boil in rice cooker, stir; titrate to +1.0 per cent, filter, and 

 sterilize as for other media. 



The above includes the more important culture media used in bacte- 

 riological work. Others can be prepared as ocasion requires. It is not 

 necessary to make up the full amounts indicated if it is evident that smaller 

 quantities will suffice. The student should prepare all of the media in 

 small amounts (one-quarter the quantities given) several times, in order to 

 get the necessary experience and practice. 



6. General Directions for the Preparation of Culture Media 



Book information alone is not sufficient. Experience must be added. 

 Also, brief, concise explanations are far more valuable than lengthy de- 

 scriptions of unessential details. Those possessed of good judgment do not 

 require lengthy explanations, and lengthy explanations would certainly be 

 wasted on those who lack good judgment. This does not imply, however, 

 that it is unnecessary to adhere strictly to established methods. The 

 novice must follow closely the methods formulated by those who have 

 devoted many years to some one particular mode of procedure, as it is 

 wholly unlikely that he can improve upon them. Furthermore, when a 

 physician calls for Loeffler's blood serum, for example, he wishes to be 

 assured that the medium has been prepared according to the standard 

 method. Any substitution or deviation, no matter how slight, may 

 bring about wholly negative or erroneous results and conclusions. With 

 this in mind the following suggestions are added: 



A. Selection of Ingredients. Great care must be observed in the selec- 

 tion of the ingredients used in the preparation of culture media. Meats 

 used must be from healthy animals, and there must be absolute certainty 

 that no preservative has been added. Buy the meat personally from 

 the nearest reliable butcher who keeps fresh meats only. Remove as 



