98 BACTERIOLOGY. 



results are to be obtained i. e., if a translucent, solid 

 medium is to result. If the old, small form of appa- 

 ratus be employed (Fig. 19), then the solidification can 

 be accomplished in a shorter time than if the larger 

 forms commonly employed are used. No definite 

 rule for the time that will be required can be laid 

 down, for this is not constant. If the small solidify- 

 ing apparatus be used, very good results may be ob- 

 tained in about two hours at 78 C. It frequently 

 requires a longer time at a higher temperature than 

 has been mentioned. This is especially the case with 

 Loeffler's serum mixture. 



The best results are obtained when a low temperature 

 is employed for a long time. Under any circumstances 

 the tubes must be observed from time to time through 

 the glass door or cover with which the solidifying oven 

 is provided, and each time the oven should be slightly 

 jarred with the hand to see if solidification, as indi- 

 cated by the disappearance of tremors from the serum, 

 is beginning. If the temperature gets too high, or the 

 exposure is too long, an opaque medium results. The 

 temperature to be observed is that of the air inside 

 the chamber, and also that of the water surrounding it. 

 The latter is usually a degree or two higher than the 

 former. The tubes should not rest directly upon the 

 heated bottom or against the heated sides of the cham- 

 ber, but should lie upon racks of wood or wire, and be 

 protected from the sides by a wire screen of gauze: in 

 this way the tubes are all exposed to about the same 

 temperature. The thermometer which indicates the 

 temperature inside the chamber should not touch the 

 surfaces, but should either be suspended free from 

 above through a cork in the top of the apparatus, if 



