40 BACTERIOLOGY. 
segments of a spiral. Here, too, we have large and 
small, slender and thick spirals. The twisting of the 
long axis, which here lies in two planes, is the chief 
characteristic of this group of bacteria. Under normal 
Fic. 8. Fic. 9. 
Medium-sized spirilla. Very large spirilla. 
conditions the twisting is equal throughout the entire 
length of the cell. The spirilla, like the bacilli, divide 
only in one direction. A single cell, a pair, or the 
union of two or more elements may thus present the 
appearance of a short segment of a spiral or a comma- 
shaped form, an S-shaped form, or a complete spiral 
or corkscrew-like form. 
Among uncommon morphological peculiarities in 
true bacteria may be mentioned dichotomy, or branch 
formation—that is, a side growth projecting from the 
bacterial cell. True dichotomous branching has occa- 
sionally béen observed in the bacilli—viz., the bacilli 
of tuberculosis, diphtheria, and glanders. 
Summary of Morphological Forms of Bacteria. 1. 
Coccus, or micrococeus. Spherical or  subspherical 
forms. 
