MORPHOLOGY OF BACTERIA. 73 



Paulsen, milk.* The capsules do not form when the 

 cultures are made on gelatin, agar, and potatoes. 



Peculiar unilateral thickenings or swellings of the 

 membrane are found in bacterium pediculatum, which 

 is described as a rare cause of the 

 "frog-spawn disease" of sugar fac- 

 tories (Fig. 6). 



In the spherical forms the outer Fia 6. -B a c t e r i u m 

 surface of the bacteria is^ almost al- pediculatum. (After 



,, . ,, , , ... Koch and Hosaus.) 



ways smooth ; in the short rods it is 

 often smooth and without appendages, but the larger 

 rod and screw forms are usually provided with single 

 or numerous thin flagella. These are sometimes dis- 

 tributed over the entire body of the bacterium, some- 

 times they form a bundle at one pole, sometimes there 

 is only a single polar flagellum. Shortly before divi- 

 sion bacteria with polar position of the flagella show 

 one flagellum or a bundle of flagella at each pole. 

 As A. Fischer clearly proved, the flagella are not 

 structures similar to the retractile and extensible 

 pseudopodia, but are true hair-like formations which 

 develop from outgrowth. In order to color the fla- 

 gella it is necessary to treat the bacteria with unusu- 

 ally powerful staining reagents. Then the mem- 



* It is not certain that pronounced capsule formation always 

 takes place in these nutrient fluids. Recently various authors 

 have called attention to the fact that capsule-like formations are 

 observed extensively among bacteria. Johne describes a method 

 by which they are easily made visible in anthrax, and distinct 

 capsules are also seen in this way in bacillus megatherium, bacillus 

 oxalaticus, etc. Babes has depicted capsules in streptococcus 

 pyogenes, and we have occasionally seen similar appearances in 

 many bacteria. Masses of bacteria which are united into mucous 

 clumps by swelling of the capsules are called " zooglcea. " 



