CULTIVATION OF BACTERIA 



63 



media, and thus possibility of contamination must always be kept in 

 mind. When it occurs upon solid media we, as a rule, easily detect it, 

 for we notice the growth at some point of bacteria of different colony 

 characteristics; but in fluid media, on account of the complete mingling 

 of the bacteria, we are not so apt to notice the additional growth. 



THE STUDY OF PURE CULTURES ix TUBED MEDIA. A few points 

 of the many which should be observed are the following: 



Gelatin stab cultures. 



A. Xon-liquefying. 



Line of puncture. 



Filiform, uniform growth, without special characters. 

 Beaded, consisting of loosely placed, disjointed colonies. 

 Arborescent, branched, or tree-like. 

 Some of these points are illustrated in Fig. 47, sketched by Chester 



B. Liquefying. 



Crateriform, a saucer-shaped liquefaction of the gelatin. 

 Saccate, shape of an elongated sac, tubular (Fig. 46). 

 Statiform, liquefaction extending to the walls of the tube. 



FIG. 47 



Showing characters of gelatin stab cultures : .4. Characters of surface elevation : 1, flat ; 2, raised ; 

 3, convex ; 4, pulvinate ; 5, capitate ; 6, umbilicate ; 7, umbonate. B. Characters of growth in depth ; 

 1, filiform ; 2, beaded ; 3, tuberculate-ecinulate ; 4, arborescent ; 5, villous. (From Chester.) 



Nutrient agar tube cultures give fewer points for observation, but 

 should be studied in the same way. The agar in the tubes is usually 

 slanted and the culture growth is not only in the stab, but along the 

 streaked surface. The characteristics of each should be noticed. 



