42 PHARMACEUTICAL BACTERIOLOGY. 



equivalent to a slightly acid reaction to phenolphthalein, at a temperature of 

 about 20° C. Most microbes develop best in media of such reaction. 



c. They must be free from living microbes and their spores, and from 



Fig. 17. — Arnold Steam Sterilizer. Boston Board of Health Form. This sterilizer 

 is square, and constructed with a side-door all in accordance with the recommendation of 

 the Boston Board of Health. Its large size makes it well suited to the requirements of 

 Board of Health laboratories, and it has been found to be very serviceable and convenient. 

 It is made of copper throughout, following the same principles as employed in the construc- 

 tion of the other sterilizers. 



Fig. 18. — Arnold Steam and Hot-Air Sterilizer for Surgical Instruments. This 

 steriHzer is a combination and portable sterilizer, so designed that instruments may be 

 both sterilized and then dried by hot air, if desired. About 100° C. can be attained with 

 the hot air by simply turning the valve shown in the illustration, which turns the steam as 

 it escapes from the chamber into the base. 



other organism. This requirement is attained by sterilization as already 

 described. Culture media contaminated with living organisms are not 

 usable in bacteriological work. 



