suRi'ACH stru(;turi:s 43 



The phasc-Lontrasr studies ot TcMiicsik, and Toincsik and Ciuex-Holzer 

 have revohitioniscd the previous concept of bacterial capsules as an amorphous 

 layer of polysaccharide or polypeptide mucus, by demonstrating that they may 

 possess an exceedingly ccMiiplex structure of alternate striations of poly- 

 saccharicie and polypeptide, perpendicular to the cell wall ; that is parallel 

 to the cross-walls, which are marked by exceptionally massive lamina, as arc 

 the poles of the bacilh. The growth of the capsule, like that of the cell wall, 

 occurs mainly at the junctions ot the cell wall and cross-walls. 



H: FLAGELLA 

 (15, 16, 21, 22, 3S, 47, 4.S, 50, SI, S3, <^'3, 77, 7^, 79, 99, roo, loi, 103, 104) 



Motility in the great majority of bacterial groups is by means ot flagella. 

 These number from one to several hundred. They may be arranged singly or 

 in small groups at the poles of the cell, in which case they render their possessor 

 very actively motile in a fluid mcdiimi, or they may be arranged in larger 

 numbers peritrichously, which is probably an adaptation to movement in 

 viscous media or on moist surfaces (Chapter IX). 



The polar flagella are approximately 26 mi in diameter, in I 'ibrio and 

 Psciidoniotias ; the peritrichous flagella may be as small as 19 ni// in Proteus. 

 Because of their small size their mode of action is difficult to determine. They 

 have been described as lashing, but more probably act by waves of contraction 

 passing down their fine coils. The wavelength of these coils varies from 

 2 to 3 /x and is constant for any bacterial species, but variants in a single strain 

 may have flagella c^f double the normal wavelength. 



Flagella ponit away from the direction of motion, and the rearmost may 

 become twisted together into a spiral thread. Cast-oft flagella, in fixed 

 preparations, also tend to knit up into whips in this manner. 



The flagella originate m the cell membrane or surface cytoplasm and pass 

 outwards through the cell wall. When the cell wall is removed by digestion 

 with lysozyme, the flagella remain attached to the protoplast. Their point of 

 origin is a basal granule or blepharoplast, approximately spherical and rather 

 larger in diameter than the flagellum which arises from it. In most bacterial 

 < genera each flagellum arises from a separate granule, but the flagellar fibrils 



