48 PHARMACEUTICAL BACTERIOLOGY. 



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

 tions of unessential details. Those possessed of good judgment do not re- 

 quire 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 sub- 

 stitution or deviation, no matter how slight, may bring about wholly neg- 

 ative or erroneous results and conclusions. With this in mind the follow- 

 ing suggestions are added: 



A. Selection of Ingredients. — Great care must be observed in the selection 

 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 much of the fat 

 as possible. The so-called round steak of beef is usually employed. 



Use only the best gelatin; the so-called best French gelatin is usually 

 employed, although much of the "French gelatin" comes from Berlin, 

 Chicago, Omaha, or other places equally remote from France. Do not 

 attempt to use old friable gelatin. 



The milk requirements have already been referred to. The milk must 

 be fresh, placed on ice at once, and sterilized within twenty-four hours 

 after it is taken from the cow. If the milk is obtained from an unknown 

 dealer, test it for the presence of added water, preservatives, and other 

 foreign matter. 



Agar does not deteriorate readily, and may be kept in good condition 

 for a long time. Other highly gelatinous seaweeds may be used, although 

 this is not permissible in the preparation of any of the standard culture 

 media. 



Serum, egg albumen, peptone, various indicators, etc., must be pure. 

 Too much caution carmot be observed in this regard. Secure the blood for 

 serum personally wherever possible, from healthy animals. Use egg albu- 

 men from fresh eggs, not from cold-storage eggs. Peptone and other chem- 

 icals should be secured from reliable dealers. 



B. Suggestions on the Preparation of Culture Media. — First of all, some 

 experience is necessary before a neat article can be prepared. Do not 

 expect to prepare a medium which meets all of the requirements the very first 

 time. In preparing gelatin media, remember that these are injured by excess- 

 ive heating, and in preparing agar media, remember that they are very difficult 



