68 INOCULATION OF CULTURE-MEDIA WITH BACTERIA. 



Give Koch's method of preparing potatoes for a culture? What are the 

 precautions necessary for protecting the potato from external germs ? 

 How would you prepare a potato test-tube culture ? 

 How would you prepare Dunham's solution? 

 How are glucose-, lactose-, and saccharose-bouillon prepared ? 



CHAPTER IV. 



THE INOCULATION OF CULTURE-MEDIA WITH 

 BACTERIA. 



THE METHOD OF INOCULATING FLUID MEDIA. 



FOR the purpose of cultivating bacteria in liquid media it 

 is only necessary to introduce the smallest possible particle 

 containing the bacteria, into the media, by means of a steril- 

 ized platinum needle (Fig. 15). For this procedure the 

 culture-tube is held slightly inclined between the thumb and 

 fingers of the left hand, its cotton plug removed by a twist- 

 ing motion and placed between the backs of the third and 

 fourth fingers of this hand, being careful not to touch that por- 

 tion of the cotton which fits inside of the tube. The inoculating 

 needle is rapidly introduced into the liquid and gently stirred 

 around, after which the cotton plug is replaced, and the plat- 

 inum needle sterilized by heating to redness in the flame. 



It is good practice to accustom one's self never to take up 

 a platinum needle, whether it is known to be inoculated or unin- 

 oculated, without first sterilizing it by heating it to redness in the 

 flame , and allowing it to cool for a few seconds before taking 

 up with it the inoculating material. The bacteria might other- 

 wise be destroyed by the heat. Again, after use the needle should 

 always be sterilized in the same manner before putting it down. 



THE METHODS OF INOCULATING SOLID MEDIA. 



1. For the inoculation of potatoes and other solid media 

 not hereafter mentioned, it is only necessary to streak the 

 surface of the medium with a platinum needle or other instru- 

 ment which has been dipped into or which contains a small 



