METACHROMATIC GRANULES 43 



7?. subtilis, tubercle bacilli, and diphtheria bacilli. However, the 

 great majority of the organisms contain chitin, a substance which 

 on hydrolysis yields glucosamin, CH 2 OH(CHOH) 3 CHNH 2 CHO, 

 and acetic acid. Chitin is typically animal in origin and for this 

 reason some have argued that the bacteria belong to the animal 

 and not to the plant kingdom. The flagella probably originate from 

 the ectoplasm. 



Capsules. Many bacteria possess a capsule which is an outgrowth 

 of the cell membrane and is composed of mucin. In stained cultures 

 it usually appears as a halo surrounding the organism. The forma- 

 tion of a capsule is not confined to only a few species, some writers 

 arguing that under appropriate conditions all organisms form them; 

 yet the so-called capsulates are especially prone to do so. Some 

 organisms produce capsules when grown on one media, but not if 

 grown on another. Milk especially favors the formation of capsules. 



Sheath. Often a distinct tube is formed in which is inclosed the 

 chain of cells; to this tube is given the name "sheath." It is espe- 

 cially characteristic of some of the trichobacteria as crenothrix in 

 which there is a deposition of iron. Sometimes these become fossil- 

 ized, occurring in hugh deposits in ferruginous water. 



Zob'glcea. Often the gelatinous material of the cell causes great 

 masses of cells to adhere to each other, to which condition is given 

 the name "zoogloea." This is especially characteristic of the nitri- 

 fying bacteria. 



Cytoplasm. Chemical analysis of the cytoplasm of the bacteria 

 cell shows it to be richer in nitrogen and phosphorus than are the 

 cells of higher plants. Moreover, on being stained the cytoplasm 

 appears as a homogeneous mass filling the whole cell, thus making 

 it certain that bacteria do not possess a nucleus in the ordinarily 

 accepted sense of the term. But the fact that the organisms stain 

 so readily with the ordinary nuclear stains has led some to believe 

 that the organisms are made up mainly of nuclear material. This 

 is the view held by Zettnow who has succeeded in staining some large 

 spirilla in a living motile condition. Hence the idea held by the 

 majority of workers at the present time is that the bacterial cell is 

 composed of small quantities of cytoplasm in which is imbedded 

 large quantities of fragmented, irregularly distributed chromatin. 



Metachromatic Granules. Some bacteria contain various granules 

 within the cell which stain differently from the substance of the cell 

 body; these are known as " metachromatic" granules or " Babes- 

 Ernst" granules, or because of their frequent position at the ends of 

 bacilli as polar bodies. Microchemical examination has shown them 

 to be composed of various substances: fat, sulphur granules, gly- 

 cogen, lecithin, and protein-like compounds. 



Their function has been variously interpreted. Some have com- 

 pared them to the centrosomes of more highly specialized cells. 



