Fig. 4. Isolated cell wall of Bacillus megaterium (x 21, 000). By cour- 

 tesy of Drs. Salton and Williams (Ref. 36). 



Fig. 5. Electron micrograph of Halobacterium halobium showing 

 hexagonally packed macromolecules in the cell wall (x 42,500). By 

 courtesy of Drs. Houwink, Mohr, and Spit. 



10 



