FLAGELLA. 23 



of these capsules appears. See also, in the special part, 

 Streptococcus involutus and niesenterioides. Extensive 

 review of literature by Binaghi, C. B. L. iv, 919. 



Characteristic unilateral thickenings or swellings o£ the bacterial 

 membrane are presented by Bact. pediculatum, which is described 

 as an uncommon cause of the ' ' frog-spawn disease ' ' of sugar factories 

 (Fig. 6). 



Regarding especially striking membrane thickening at the ends of 

 threads (club formation), see those of actinomycetes. 



The outer surface of bacteria is often perfectly smooth 

 and without appendages in the short bacilli, and almost 

 always in the spherical forms, but the longer rods and spiral 

 forms are usually provided with delicate single or multiple 

 flagella. These are often distributed over the whole body 

 of the bacterium, often form only a little bunch at one end, 

 and often there is found but a single polar flagellum. Bac- 

 teria with polar flagella, shortly before division, show a 



Fig. 6. — Bact. pediculatum (after Koch and Hosaus). 



single flagellum or a bunch of flagella at each end. As A. 

 Fischer particularly showed, flagella are not of the nature of 

 retractile and extending pseudopodia, but true hair-like 

 outgrowths. For the demonstration of flagella it is neces- 

 sary to treat the bacteria with especially powerful staining 

 agents. In this process the capsules of the bacteria, which 

 remain unstained in the ordinarj' method, are stained, and 

 so the bacteria appear very much thickened. Occasionally 

 wide layers of capsule remain unstained and the flagella 

 are then set upon a narrow ring-like halo, separated from 

 the bacillus by a colorless zone (Zettnow, von Stocklin, 

 A. Fischer). Unfortunately, very many of the procedures 



made plainly visible ; also in this manner distinct capsules are obtained 

 in B. megatherium, oxalaticus, etc. Babes has depicted capsules in 

 connection with the Streptococcus pyogenes, and we have ourselves 

 occasionally seen similar formations in the case of many bacteria. 



Masses of bacteria which are united into mucous clumps by swelling 

 of the capsules (often a sign of death) are called " ZOOglea." 



