BLOOD-SERUM. 465 



lower temperature than that mentioned. A temperature of 

 58 maintained for an hour will destroy, as a rule, actively 

 growing bacteria. The spores, of course, are not affected 

 by this heat. They must be given an opportunity to ger- 

 minate, in which case the resistant spore is converted into 

 a relatively weak, vegetating form. When this takes place 

 the latter promptly yields to the temperature employed. 

 It should be remembered, however, that there are bacteria 

 which, far from being killed, actually thrive at this tem- 

 perature '(p. 72). If these should happen to be present it 

 will be impossible to sterilize the serum by this method. 

 The sterilization of the serum tubes can best be accom- 

 plished by the "use of a Roux water-bath. This exceedingly 

 useful apparatus is shown in Fig. 64, and as shown, it is 

 provided with a Roux metallic thermo-regulator (R). A 

 wire basket (D) is immersed in the water and is provided 

 with an adjustable bottom (E). In this way the tubes can 

 be immersed in water to any desirable depth. The cover 

 (C) is double- walled and filled with water. Through the 

 opening on the top a thermometer is inserted into the liquid. 



The wire basket, as ordinarily supplied with this apparatus, is 

 provided with a movable bottom which is clamped to the central 

 tube. The latter takes up desirable space and it is advisable, there- 

 fore, to alter the basket so that the bottom can be clamped, on the 

 under side, to runners fastened on the inner surface of the wire 

 basket. The thermometer and mercury thermo-regulator (Fig-. 37, 

 p. 246), can be suspended to advantage in the side compartment which 

 is intended for the metallic regulator. 



The serum tubes are sterilized in this apparatus by 

 heating at 58 for one hour on each of six consecutive days. 

 The interval between heating may be shortened to 10 hours 

 if the tubes, after each heating, are placed for 2-3 hours at 

 37. This will assist the germination of the spores present. 

 The tubes are then kept at the ordinary room temperature 

 for about eight hours, after which they are submitted again 

 to a heat of 58. 



30 



