18 MORPHOLOGY OF BACTERIA. 



it is possible to distinguish the nucleus with a high-power 

 lens (y 1 ^ oil immersion). The extreme minuteness of bacteria 

 is more or less of an obstacle to making studies of their real 

 appearance. 



Some bacteria (Bacillus Megaterium) contain also very 

 deeply staining granules. These granules are of two kinds : 

 metachromatic granules, which are believed to be the result 

 of a degenerative process ; and polar granules, which are still 

 a matter of speculation. It was discovered recently that the 

 protoplasm of many bacteria also contains fat droplets. This 

 tinding may possibly be of service in differentiating certain 

 organisms. 



Cell-membrane : The cell-membrane is usually quite thin, 

 but it may be of such thickness as to resemble a distinct cap- 

 sule or envelope of mucus. Such a capsule is seen to best ad- 

 vantage enclosing the pneumococcus when the germ is exam- 

 ined in the sputum of an individual suffering from lobar 

 pneumonia. The capsule is seen rarely when the organism is 

 grown artificially. This is true of all pathogenic bacteria. 

 Special reagents and stains must be used for the demonstra- 

 tion of this capsule. The methods w r ill be described later, in 

 the chapter on Microscopic Examination of Bacteria. 



Flagella and Motility : Many varieties of bacteria have 

 very delicate projections of the cell-membrane, called flagella, 

 which appear to be organs of locomotion. So far as their 

 appearance is concerned, they correspond to the cilia of an 

 epithelial cell. Some bacteria have only one or more terminal 

 flagella (Fig. 1), while others have both terminal and lateral 

 flagella. The number varies from one terminal flagellum 

 monotrichia ( Vibrio cholerce), to two or more at each end 

 lophotrichia (Bacterium syncyaneum}. Organisms with both 

 terminal and lateral flagella belong to the class peritrichia 

 (Bacillus typhosus). These flagella, with one exception 

 (Micrococcus ayilis of Ali-Cohn), are seen only on the rod- 

 shaped or spiral bacteria. The most active bacteria usually 

 have the greatest number of flagella, although there are a few 

 bacteria which are well supplied with flagella and yet are 

 devoid of motility ; and others with few flagella are actively 

 motile. It has been suggested that the flagella, in addition 



