PREPARATION OF NUTRIENT AGAR 41 



gelaticus n. sp. (gran) and Bad. nenckii, both of which are 

 found, as would be expected, in sea water. This compara- 

 tive inertness of agar renders it valuable for the preparation, 

 of solid synthetic media, the value of which may be en- 

 hanced by subjecting the commercial agar to natural 

 fermentation during which process any traces of avail- 

 able food substances are used up by the microorganisms 

 present. (Beijerinck.) 



Agar is of special use in bacteriological work in which 

 the cultivation of microorganisms must be conducted at a 

 temperature above the melting-point of gelatin. This 

 feature has made possible the great strides that have been 

 taken in medical bacteriology, as many pathogenic bacteria 

 can be isolated and grown only with difficulty at tempera- 

 tures below that of the body. 



REFERENCES 



SMITH, ERWIN F.: Bacteria in Relation to Plant Diseases. Vol. I, 



pp. 31-36. Several illustrations. 

 SCHULTZ, N. K.: Zur Frage von der Bereitung einiger Nahrsubstrate. 



Cent. f. Bakt. I. Orig., Bd. 10, 1891, p. 57. 



EXERCISE 9. PREPARATION OF NUTRIENT AGAR 



Apparatus. 3.5 liter agate-ware pail; 15 gms. agar; 

 10 gms. peptone; 5 gms. salt; 10 gms. egg albumen (or one 

 egg); 500 c.c. sterile meat infusion; 500 c.c. tap water; 

 titration apparatus; N/20 NaOH; N/l NaOH; phenol- 

 phthalein (indicator); distilled water; large funnel; 

 plaited filter paper; filling funnel; sterile test tubes; 

 sterile liter flask; coarse balances; large gas burner; 1 

 liter measuring cup; apparatus for steam sterilization. 



Method. 1. In a 3 liter agate ware pail place 15 gms. 

 of agar in 500 c.c. of tap water. 



2. Wash the agar well, separating the shreds and squeez- 

 ing it through the hands. 



3. Decant the dirty water, measuring the amount poured 



