122 DISINFECTION— STBRILIZA TION— DISINFECTANTS 



destructive to bacteria than continuous heating for the same 

 length of time, but the development of the spores is the most 

 important factor. Discontinuous heating may also be used 

 at temperatures below the boiling-point for the sterilization 

 of fluids like blood serum which would be coagulated by 

 boiling. In this case the material is heated at 55° to 56° 

 for one hour, but on each of seven to ten successive days. 

 The intermittent heating and cooling is of the same impor- 

 tance as the development of the spores in this case. (Better 

 results are secured with such substances by collecting them 

 aseptically in the first place.) 



Fig. 77. — The Arnold steam sterilizer for laboratory use. 



Steam. — Steam is one of the most commonly employed 

 agents for sterilization and disinfection. It is used either 

 as "streaming steam" at air pressure or confined under 

 pressure so that the temperature is raised. For almost all 

 purposes where boiling is applicable streaming steam may 

 be substituted. It is just as efficient and frequently more 

 easily applied. The principle of the numerous forms of 

 "steam sterilizers" (Fig. 77) is essentially the same. There 



