FLAGELLUM 29 



pig's blood and in rat's blood). The presence of capsules 

 around an organism can be proved only by staining the 

 capsule. Many bacteria when stained in albuminous fluids 

 show a clear space around them which appears like a cap- 

 sule. It is due to the contraction of the fluid away from the 

 organism during drying. 



Metachromatic Granules.— The term ''metachromatic" is 

 applied to granules which in stained preparations take a 

 color different from the protoplasm as a whole (Fig. 21). 

 They vary widely in chemical composition. Some of them 

 are glycogen, some fat droplets. Others are so-called "gran- 

 ulose" closely related to starch but probably not true 

 starch. Others are probably nuclein. Of many the chemical 

 composition is unknown. They are called ''Babes-Ernst 

 corpuscles" in certain bacteria (typhoid bacillus). Since 

 they frequently occur in the ends of cells the term "polar 

 granules" is also applied. Their presence is of value in the 

 recognition of but few bacteria ("Neisser granules" in 

 diphtheria bacilli). 



Fla>gellum.— A flag ellum is a very minute thread-like pro- 

 cess growing out from the cell wall, probably filled with a 

 strand of cytoplasm. The vibrations of the flagella move 

 the organism through the liquid medium. Bacteria which 

 are thus capable of independent movement are spoken of 

 as "motile bacteria." The actual rate of movement is very 

 slight, though in proportion to the size of the organism it 

 may be considered rapid. Thus, Alfred Fischer determined 

 that some organisms have a speed for short periods of about 

 40 cm. per hour. This is equivalent to a man moving more 

 than 200 miles in the same time. 



It is obvious that bacteria which can move about in a 

 liquid have an advantage in obtaining food, since they do 

 not need to wait for it to be brought to them. This advan- 

 tage is probably slight. 



An organism may have only one flageflum at the end. It 

 is then said to be monoirichic (Fig. 22) {/^oi^o-, monos = alone, 

 single; '^no-^ trichos = hair). This is most commonly at the' 

 front end, so that the bacterium is drawn through the liquid 

 by its motion. Rarely it is at the rear end. Other bacteria 



