Laboratory Outline for General Bacteriology 



Bacteria move by means of flagella. These are slender, hair- 

 like processes usually several times as long as the bacterial cell. 

 Some species have but one on the end, monotrichiate ; some have 

 a tuft on one end, lophotrichiate ; some have them distributed all 

 over the organism, peritrichiate. The arrangement of the flagella 

 causes a difference in the kind of motion. Special staining methods 

 are necessary in order to see the flagella. 



Examine No. 19 B. mesentericus 



32 M. agilis 



" 129 M. lactis varians 

 20 B. proteus 

 48 B. pullorum 

 23 B. mycoides 



Examine preparation from a cake of yeast. Make drawings 

 showing appearance of yeasts, starch grains, and bacteria. 



GELATIN 



Gelatin serves two purposes. As a solid culture medium, it is 

 a technical device by which the isolation of a single species of 

 microorganism is made possible. To those organisms which secrete 

 proteolytic enzymes it serves as a nitrogenous food material. Beef 

 extract and peptone are added as food for bacteria. 



Gelatin was the first substance used for a solid culture medium. 

 This medium was originated in 1882 by Koch and has since revolu- 

 tionized the science of microbiology. Milk sugar and litmus are 

 also added when acid production is to be determined. 



Gelatin media will melt at a temperature of about 24 C to 26 C 

 solidifying again at 20C to a clear transparent jelly. 



Gelatin plates do not have to be inverted during incubation, as 

 do the agar plates, because no water of condensation ordinarily 

 collects on the cover of the Petri dish in case of the gelatin. 



AGAR 



Agar is a seaweed product used in preparing various kinds 

 of solid culture media. Ordinarily agar is composed of beef extract, 

 peptone and agar. It becomes fluid at about 85 C and solidifies 

 below 40 C C, becoming a very solid opaque jelly, which retains its 

 shape well in slants and plates. 



Agar is commonly used in determining the number of bacteria 

 per cc. in milk, water, and various other substances. A definite 



17 



