EL O OD-SER UM. 123 



76-80 C. In solidifying the serum the tubes should 

 be placed in an inclined position, so that as great a sur- 

 face as possible may be given to the serum. The proc- 

 ess of solidification requires constant attention if good 

 results are to be obtained i. e. 9 if a translucent, solid 

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

 ratus be employed (Fig. 19), 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 

 Loffler's serum-mixture. 



The best results are obtained when a low temperature 

 is employed for a long time. Under any circumstances 

 the tubes should 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 or gauze : in 

 this way all the tubes are exposed to about the same 



