14 GENERAL MORPHOLOGY AND BIOLOGY 



in packets of four (called tetrads) of sixteen may be found, the 

 former number being the more frequent. To all these forms 

 the word micrococcus is generally applied. . The individuals 

 in a growth of micrococci often show a tendency to remain 

 united in twos. These are spoken of as diplococci, but this is 

 not a distinctive character, since every coccus as a result of 

 division becomes a diplococcus, though in some species the 

 tendency to remain in pairs is well marked. The adhesion of 

 cocci to one another depends on the character of the capsule. 

 Often this has a well-marked outer limit (micrococcus tetragenus), 

 sometimes it is of great extent, its diameter being many times 

 that of the coccus (streptococcus mesenterioides). In none of 

 the cocci have endogenous spores been certainly observed. , The 

 species of the streptococci and staphylococci differentiated 

 number several hundreds. Usually included in this group are 

 coccus-like organisms which divide in three axes at right 

 angles to one another. . These are referred to as sarcinae. If 

 the cells are lying single they are round, but usually they are 

 seen in cubes of eight with the sides which are in contact 

 slightly flattened. Large numbers of such cubes may be lying 

 together. The sarcinae are, as a rule, rather larger than the 

 other members of the group. Most of the cocci are non-motile, 

 but a few motile species possessing flagella have been described. 

 2. Bacilli. — These consist of long or short cylindrical cells, 

 with rounded or sharply rectangular ends, usually not more than 

 1 /a broad, but varying very greatly in length. They may be 

 motile or non-motile. Where flagella occur, these may be 

 distributed all round the organism, or only at one or both of 

 the poles. Several species are provided with sharply-marked 

 capsules (b. pneumoniae). In many species endogenous spolia- 

 tion occurs. The spores may be central, terminal or subterminal, 

 round, oval, or spindle-shaped. There is no doubt that among the 

 bacilli in certain cases, e.g., in b. diphtheriae and b. tuberculosis,' 

 the phenomenon of true branching may occur. Such instances 

 form a connecting link between the bacilli and the higher 

 bacteria, e.g., streptothrices. 



Great confusion in nomenclature has arisen in this group in con- 

 sequence of the different artificial meanings assigned to the essentially 

 synonymous terms bacterium and bacillus. Migula, for instance, applies 

 the former term to non-motile species, the latter to the motile. Hueppe, 

 on the other hand, calls those in which endogenous sporulation does 

 not occur, bacteria, and those where it does, bacilli. In the ordinary 

 terminology of systematic bacteriology the word bacterium has been 

 almost dropped, and is reserved, as we have done, as a general term for 

 the whole group. It is usual to call all the rod-shaped varieties bacilli. 



