EXPLANATION OF THE PLATE. 



FIG. I. A large mass of bacteria growing in a tube on a trans- 

 parent culture medium. This species is called Micrococcus luteus, 

 (page 40) and is a " pure culture " (page 35). 



FIG. II. A gelatin plate culture (pages 36, 37, and 38), showing 

 several colonies of different species of bacteria growing in the thin 

 layer of solidified gelatin. Each colony is composed of thousands of 

 individual bacteria. (See Fig. v.) 



The yellow colonies are those from which a small portion was 

 taken on the end of a sterilized needle and planted in the tube 

 shown after a few days growth in Fig. I. 



The tube and plate in Figs I. and II. are represented of about one 

 third the natural size. 



Fig. III. Several different forms of bacteria represented as they 

 look when stained with one of the anilin dyes and magnified about 

 i, CKDO times (see pages 15, 39, and 40). 



Nos. i and 2 : Micrococci, single and in pairs. No. 3 : Micro- 

 cocci in chains, called streptococci. No. 4 : Tetrads of micrococci. 

 Nos. 5, 6, 7, and 8 : bacilli, showing different sizes and groupings 

 in No. 5, cilia are seen at the ends of some of the bacilli (page 16). 

 Nos. 9 and 10 : spiral bacteria ; those in No. 9 with cilia. Nos. 

 II and 12 : bacilli with spores (page 19). 



FIG. IV. A cell in which are seen seven long slender bacilli 

 magnified about 3,000 times. 



FIG. V. A single colony as seen under a low power of the 

 microscope on the plate culture, Fig. II. This is magnified about 

 20 times. 



