02 CLINICAL BACTERIOLOGY. 



first and the second dilution are poured upon plates in the 

 same way ; a second and a third glass shelf placed upon the 

 first in the moist chamber, and a plate respectively placed 

 upon each of these. 



This original method of Koch for pouring plates, which 

 is still used in certain investigations, has been replaced by 

 a simpler and more convenient method : In place of the 

 plates double dishes of glass are used (Petri dishes, Fig. 23). 

 Sterilization, liquefaction, and inoculation of the tubes are 

 effected exactly in the same way. After inoculation, how- 

 ever, the liquefied gelatin of the three tubes is simply 

 poured into three sterile dishes, which are then covered and 

 left to themselves. 



In accordance with the bacteria that it is desired to cul- 

 tivate, and the temperature that prevails in rooms, the fin- 

 ished plates that is, those that have been solidified are 

 placed at room-temperature in a dark place, or in the 



Fig. 23. Petri dish for making plate-cultures. 



thermostat at a temperature at from 24 C. (75.2 F.) to 

 26 C. (78.8 F.). To protect the plates from the drying 

 influence of the air, which inhibits the growth of the 

 bacteria, it is useful to preserve them in so-called culture- 

 boxes. Each of these consists of a four-cornered box of 

 sheet-iron covered with a glass lid, and which is converted 

 into a moist chamber by the introduction of a dish con- 

 taining moistened cotton (Forster). 



The method described suffices when all that is desired is 

 the determination whether bacteria are present in material 

 submitted for examination, as well as their nature. If, 

 however, the number of bacteria present is to be accurately 

 determined also quantitatively, the following mode of pro- 

 cedure is adopted : Into a gelatin-tube containing exactly 

 ten cubic centimeters, after liquefaction a given amount of 

 the material to be examined is introduced either by means 

 of a sterile pipet (capillary pipet) or with a platinum loop 



