78 BOTANY 



Phosphorescence. The phenomena of phosphorescence, sometimes 

 seen in decaying substances, are often due to the presence of Bacteria. 



Artificial Cultures of Bacteria 



The recognition of the great importance of Bacteria has led to extensive devel- 

 opment of methods of cultivating them artificially. It is possible, with care, to 

 isolate most forms, and grow them in sterilized culture-media, from which all 

 other forms are excluded. The medium may be either liquid, like milk or 

 meat-broth, or the nutritive substance is mixed with gelatine or some similar 

 substance which solidifies when cold. When a pure culture of any species is 

 established, it is a simple matter to propagate it indefinitely. The cultivation of 

 Bacteria is not only important in the study of disease germs, but it is possible 

 to isolate the specific Bacteria which flavor butter, cheese, etc. , and by introduc- 

 ing these into the butter or cheese while it is being made the flavor may be 

 controlled. 



Classification of Bacteria (Migula, 12) 



Ord. I. Eubacteria. Colorless, or occasionally chlorophyll-bearing 

 forms, without central-body. 



Fam. 1. Coccacese. Cells non-motile, globular. Divisions 

 in 1, 2, or 3 planes ; Micrococcus, Sarcina, etc. 



Fam. 2. Bacteriaceae. Cells more or less elongated, with- 

 out sheath ; motionless or ciliated. Bacterium, Bacil- 

 lus, etc. 



Fam. 3. Spirillaceae. Cells elongated, curved or spiral, 

 without sheath ; usually motile. Spirillum. 



Fam. 4. Chlamydobacteriacese. Cells in chains, sur- 

 rounded by a common sheath. Cladothrix, Crenothrix, 

 etc. 



Ord. II. Thiobacteria. Kelatively large forms, usually showing a 

 central-body, and sometimes purple pigment, but no 

 chlorophyll. Sulphur Bacteria. 



Fam. 1. Beggiatoaceae. Filamentous forms without pig- 

 ment. 



Fam. 2. Rhodobacteriacese. Cells of various forms, 

 globular, rod-shaped, or spiral, containing purple 

 pigment, bacterio-purpurin. 



The Myxobacteriaceae (Thaxter, 21, 22) 



The Myxobacteriaceae are forms which are undoubtedly related to 

 the Bacteria, of which they may perhaps constitute a third order. Our 

 knowledge of these interesting forms is due largely to the researches 

 of Professor Thaxter. They consist of minute cells, closely resem- 

 bling typical Bacteria, but the cells are united into structures of very 



