M TRIKM 1501 II i 15 



Arnold or an autoclave. (This sterilization in the rice cooker makes 

 the media too dry.) 



In making media a rice cooker is almost essential; at any rate, it is 

 so if ease, expedition and unfailing success in preparation are to be 

 achieved. As it is necessary to make the contents of the inner com- 

 partment boil, the temperature of the water in the outer compartment 

 must be raised. This is done by using a 25% solution of common salt 

 or a 20% solution of calcium chloride in the outer compartment instead 

 of plain water. 



A 15% solution of salt raises the boiling point 2 1/2 C.; a 20%, 

 3 1/2 C., and a 25%, 4 1/2 C. The raising of the boiling- 

 point by calcium chloride is about the same for similar strength 

 solutions. 



Although the Bacteriological Committee of the A. P. H. Asso- 

 ciation recommends special steps to be taken in the preparation of 

 gelatin and agar, yet for clinical purposes it will be found satisfactory 

 to keep on hand a stock of bouillon, and when it is desired to make 

 agar or gelatin to simply prepare such media from the stock bouillon 

 in the way to be subsequently given. 



XUTRIEXT BOUILLON. 



This may be made either from fresh meat or from meat extract. 

 Media from fresh meat are usually lighter in color and possibly clearer. 

 In the Philippines, however, certain measures employed for the preser- 

 vation of the meat made it very difficult to prepare clear bouillon from 

 it, so that meat extract was used entirely. There is very little differ- 

 ence, if any, in the nutritive power of media made in either way. 

 The chief objections to fresh meat as a base are: (i) It takes more 

 time and trouble. (2) The reaction, due to sarcolactic acid and acid 

 salts, is quite acid, so that it is necessary to titrate and neutralize the 

 excess of acidity. (3) The reaction of the finished media tends to 

 change unless the boiling at the time of making was very prolonged. 

 (4) It is not infrequent to have a heavy precipitate of phosphates 

 thrown down at the time of sterilization, thus making it necessarv to 

 repeat the process of filtration and sterilization. 



