94 BACTERIOLOGY. 



can be accomplished in a shorter time than if the larger 

 forms, which are now frequently 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 

 solidifying apparatus be used, very good results may be 

 obtained 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 indicated 

 by the disappearance of tremors from the serum, is be- 

 ginning. If the temperature gets too high, or the ex- 

 posure 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 chamber, 

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

 tected from the sides by a wire screen of gauze ; in this 

 way the tubes are all exposed to about the same tem- 

 perature. The thermometer which indicates the tem- 

 perature inside the chamber should not touch the sur- 

 faces, but should either be suspended free from above 

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

 form of apparatus be used, or should lie upon a rack of 

 cork or wood, its bulb being free and a little lower than 

 the other extremity, if the small, old-fashioned appa- 



