THE INCUBATOR AND ACCESSORIES. 243 



pared in the quantities indicated below. The other half will prepare 

 the same media using-, however, commercial meat extract instead of 

 fresh beef. The method is as follows: 



To 1000 c.c. of water add 10 g. of dry pepton (Witte's), 5 g. of com^ 

 mon salt, and 2.5 g. of Liebig's meat extract, 1 warm till solution re. 

 suits, then alkalize according- to the directions given (p. 234). Boil for 

 half an hour and replace the water lost by evaporation, then filter. 



Take 100 c.c. of the bouillon and fill into the small sterilized test- 

 tubes, using 1 a small funnel, to a depth of li inches = ordinary bouil- 

 lon. 



To 100 c.c. of the bouillon, add 2 per cent, of glucose and warm till 

 dissolved. Then fill this into test-tubes = glucose bouillon. 



To the remainder (800 c.c.), add 2 per cent, of finely cut ag-ar and 

 boil over a flame till it dissolves. Then sediment and filter according 

 to the directions already given (p. 236). 



To 100 c.c. of the filtered agar, add 5 per cent, of pure glycerin 

 and mix thoroughly. Test the reaction in order to make sure that it 

 is alkaline. Finally, fill into small, sterilized test-tubes = glycerin 

 agar. 



To 100 c.c. of the filtered agar, add 2 per cent, of glucose and warm 

 till it dissolves. Then fill into tubes to a depth of about 2 inches = 

 glucose agar. 



Transfer the remainder of the agar to sterilized test-tubes = or- 

 dinary agar. The several bouillon and agar media are then fraction- 

 ally sterilized (p. 162). 



The Incubator. 



In cultivating pathogenic organisms it is advisable to 

 grow these, whenever possible, at the temperature of the 

 body. In this way, they are supplied with one of the con- 

 ditions under which they live in nature. A few organisms, 

 notably the tubercle bacillus and the gonococcus, will show 

 no growth at the ordinary temperature. In such instances, 

 it is absolutely necessary to use a higher temperature in or- 



1 Most any of the commercial meat extracts will answer equally 

 well. A nutrient gelatin can be prepared with such extracts in the 

 same way as agar. 



