EXAMINATION OF CULTURES 109 



the surface of the medium have overgrown the more delicate 

 or less vigorously growing ones. It is important also to note 

 the difference between the colonies on the surface, in the 

 depth of the medium, and at the bottom. In case of gelatin 

 plates it is necessary to watch them carefully in order to 

 detect the early appearance of liquefying colonies. The 

 examination of plate cultures, therefore, consists in deter- 

 mining the character of the different colonies, their action 

 upon the medium, the rapidity of their development, and in 

 case of quantitative analysis, the number and variety of 

 colonies. This is nearly always required in the analysis of 

 milk, water, feces or other substances. In describing the 

 colonies, Chester's 1 terminology is valuable. 



Chester's terminology for description of colonies. 



1. Form of colonies. Plate culture. 



Punctiform: dimensions too slight for defining form by naked 



eye, minute, raised, semispherical. 

 Round: of a more or less circular outline. 

 Irregular. 

 Elliptical. 



Fusiform: spindle-shaped, tapering at each end. 

 Cochleate: spiral or twisted like a snail shell. 

 Ama'boid: very irregular, streaming. 

 Mycelioid: a filamentous colony with the radiate character of a 



mold. 



Filamentous: an irregular mass of loosely woven filaments. 

 Floccose: of a densely woolly structure. 

 Rhizoid: of an irregular branched, rootlike character, as in 



Bact. mycoides. 



Conglomerate: an aggregate of colonies of similar size and form. 

 Toruloid: an aggregate of colonies like the budding of the yeast 



plant. 

 Rosulate: shaped like a rosette. 



2. Detailed character of surface. 



Smooth: surface even, without any of the following distinctive 



characters. 

 Alveolate: marked by depressions separated by thin walls, so as 



to resemble a honeycomb. 

 Punctate: dotted with punctures like pin pricks. 



1 Chester. A Manual of Determinative Bacteriology. 1901. 



