STERILIZATION. 



47 



sterilized by steaming twenty to thirty minutes on three consecutive days, but will 

 develop bacterial growths when put into the thermostat. If such were really the 

 case, milk would be one of the worst of cnltnre-media instead of one of the best. 

 The general experience of bacteriologists is not in accord with this statement. 

 Occasionally, in my own experience, a single steaming of five or ten minutes has 



sufficed to sterilize milk 

 completely, at least so far as 

 relates to organisms which 

 grow aerobically and at tem- 

 peratures under 4oC. Such 

 milks have remained un- 

 changed for two or three 

 months at room tempera- 

 tures (20 to 25 C.), and 

 also in the thermostat at 

 blood heat. For anaerobes, 

 or organisms which will 

 grow only at temperatures 

 above 40 C., I have not 

 tested. 



One possible source ol 

 error in the use of steam 

 for sterilization is ignorance 

 of the exact temperature of 

 the steam-chamber. Every 

 steam-sterilizer should have 

 a hole punched through the 

 top, into which is fitted a 

 cork through which a ther- 

 mometer projects into the 

 chamber. In this way may- 

 be determined beyond doubt 

 for just how many minutes 

 the media has been exposed 

 to steam at 100 C. The 

 Arnold steam - sterilizer, 

 which is one of the best,t 

 is greatly improved by this 

 simple device (fig. 42 and 

 pi. 6). In this sterilizer there is a double bottom under the water-pan. The lower 

 bottom is in contact with the Bunsen flame. Through small holes in the upper 



*Fic. 43. Improved Lautenschlager centrifuge. Capacity, 540 cc. Revolutions per minute, 

 3,000 to 4,000. It requires about 3 horsepower to run the apparatus at this high speed. About one- 

 eleventh natural size. 



(This remark does not apply to the Arnold combination steamer and dry oven, which can not 

 be recommended. 



Fig 43.* 



