CULTURE MEDIA. 



97 



PREPARATION AND CARE OF CULTURE SIEDIA. 



Everything should be carefully weighed or measured. Everything should be 

 clean as possible to begin with. By water is usually meant distilled water, and 

 this should be free from copper or other germicidal metals (see Bolton, Bibliog., 

 XXXVIII). Moore & Kellerman have shown very recently that the Bacillus 

 typhosus is destroyed in distilled water if the merest trace of metallic copper is 

 present. Water swarming with this organism was sterilized simply by standing three 

 hours in a copper vessel. The writer found the count of Bacillus tracheiphilus reduced 

 over 30 per cent by exjDOSure in bouillon in block-tin tubes for twenty-one hours. 

 Exposure for forty-eight hours gave the same result, /. <?., 33 per cent destroyed. A 

 simple glass still is shown in fig. 82. As far as possible the chemicals should be 



Fig. 82.* 



c. p., and in many cases it is necessary to make the test for oneself, no matter what 

 the reputation of the firm or the statement on the label. When possible, broken 

 packages should be avoided. It is therefore best to procure most chemicals in 

 several small packages rather than in one large one. If the preparation of culture 

 media is broken off before its completion, by nightfall or interruptions of any kind, 

 the unsterilized or incompletely sterilized media should be put into the ice-box, 

 especially if it is warm weather. Neglect of this precaution frequently results in the 

 spoiling of the media. In steam sterilization one should begin to count time only 

 after the thermometer registers 100° C, or at least 99° C. Those who live in high 



*FiG. 82. — Portion of a work-talile showing method of distilling water for use in making culture 

 media. The flasks should be insoluble glass. The cold hydrant water passes through the condenser 

 in the direction of the arrow. In actual use the upright flask and the flame are sheltered from air- 

 drafts by sheet asbestos. One-ninth actual size. 



