46 



GENERAL MICROBIOLOGY 



tures prepared in this way are also frequently termed 

 streak cultures. The term streak cultures may also be 

 applied to cultures made similarly but grown on a horizon- 

 tal flat surface as in a Petri dish. 



Slant or streak cultures are valuable in offering a large 

 surface for growth, to aerobic organisms. 



Stab (or Stich) culture is the 

 term applied to a culture, generally 

 a pure culture, which is prepared 

 by stabbing a translucent, liquefi- 

 able solid medium to a considerable 

 depth with a contaminated straight 

 needle. Gelatin stab cultures are 

 invaluable for studying gelatin 

 liquefaction. Agar is frequently 

 used for stab cultures. If sugar is 

 added to the medium, gas produc- 

 tion may be demonstrated. Aerobic 

 and anaerobic bacteria may be 

 easily differentiated by their be- 

 havior in stab culture. 



Liquid cultures are cultures 

 grown in a liquid medium such as 

 milk, broth, cider, wort, etc. 



Shake cultures are made by 



FIG. 11. Liquefaction of inoculating with a pure or mixed 

 culture, a liquefied nutrient me- 

 dium (40-45 C.). The inoculum 

 is distributed immediately through- 

 out the medium by means of the needle used, or by rotat- 

 ing or shaking. 



This type of cultivation is valuable for determining the 

 oxygen relation of the organisms introduced and is espe- 

 cially useful for demonstrating the presence of gas-producing 

 organisms if a suitable medium is used. 



Care of Cultures. 1. Incubation: Cultures should b. 



Gelatin, Saccate becom- 

 i n g Infundibuliform. 

 (Orig. Northrup.) 



