34 APPLIED BACTERIOLOGY 



three hours, whilst they were destroyed in fifteen minutes 

 by steam at 110° to 120° C. 



A number of substances cannot be heated above 100° C, 

 in consequence of chemical changes brought about ; among 

 these may be mentioned the sugars, urea, albuminoids, etc. 



Discontinuous or Intermittent Sterilisation. — In the case of 

 certain substances, such as blood-serum, hydrocele fluid, 

 etc., it is necessary to effect sterilisation below the tempera- 

 ture of coagulation of albumin. This consists of heating to 

 a temperature of from 54° to 65° C, for three or four hours 

 daily for about a week. This is best done in a special 

 incubator or a bath of warm water, the heat of which is 

 controlled by a thermo-regulator. 



Sterilisation by Chemical Agents. — In addition to the 

 usual methods of sterilisation by means of dry heat and 

 steam, various chemicals may be employed for the purpose 

 of sterilizing media and implements. For washing instru- 

 ments, and in the case of experiments on animals for locally 

 washing the body before making an incision, either for 

 inoculation or dissection in the autopsy, a solution of 1 

 in 1,000 of corrosive sublimate or 1 in 30 solution of 

 phenol is the germicide generally used. Chloroform is 

 particularly suitable for the sterilisation of blood-serum, 

 as it has a powerful germicidal action combined with a low 

 boiling-point, so that it can be driven off with certainty 

 after sterilisation is complete. As Globig has shown, it is 

 impossible by heat to free blood serum from the organisms 

 which do not grow below 50° C, and are capable of with- 

 standing a temperature of 70° C. To sterilise by this 

 method, the liquid under treatment is shaken up with 

 chloroform, and allowed to stand some days, after which 

 the mixture is freed from chloroform by prolonged heating 

 at 62° C. The boiling-point of chloroform is 61 2° C. In 

 all operations in which chemical agents are used for sterili- 



