Simulation of the cell cycle and development of a population of cells is possible because Higgins and G. D. Shockman made numerous measurements of the pole shape with an electron microscope. The cell composition is fairly constant throughout the cell cycle; thereore, unless special circumstances obtain, the rate of macromolecular synthesis is proportional to the cell size. The distributions correspond to the typical pattern of morphological development of a slowly growing culture. In this case, just after a division event, U-phase cells quickly initiate a primary growth zone. At faster growth rates, secondary growth sites develop in two waves. The formation of a first secondary site is indicated by the distribution of first secondary small sites, but later, before the primary sites of these cells have a finished pole formation, a wave of second secondary small sites is evident.

Whenchloramphenicol was addedtoa culture ofBacillus subtilis inearlyexponential growth, microscopic observation ofcells stained by4',6-diamidino-2-phenylindole showednucleoids thathadchanged inappearance fromirregular spheres anddumbbells tolarge, brightly stained spheres andovals. Incontrast, theaddition of chloramphenicol tocultures inmid-andlate exponential growth showedcells withelongated nucleoids whose frequency andlength increased astheculture approached stationary phase. Thekinetics ofnucleoid elongation after theaddition ofchloramphenicol toexponential-phase cultures was complex. Immediately after treatment, therateofnucleoid elongation was veryrapid. Thenucleoid thenelongated steadily forabout4min,after whichtherateofelongation decreased considerably. Nucleoids ofcells treated with6-(p-hydroxyphenylazo)- uracil (aninhibitor ofDNA synthesis) exhibited theimmediate rapidelongation upon chloramphenicol treatment butnotthesubsequent changes. Theseobservations suggest thataxial filament formation during stationary phase(stage Iofsporulation) intheabsence ofchloramphenicol results fromchanges innucleoid structure that areinitiated earlier, during exponential growth. Manyinvestigators havesought todescribe thearrange- mentofthenucleoplasm intheprocaryotic cell. Thesubject hasremained elusive, partly because thenucleoid undergoes rearrangement during themostgentle manipulations (e.g., rapidfiltration andtemperature changes, etc.(8)). Thus, after decades ofeffort, onlya fewnoncontroversial state- mentscan bemade:thenucleoid oftheexponential-phase cell islocalized primarily inthecenterofthecellbutdoes extend totheperiphery ofthecytoplasm (2,7,8,12,13); in stationary-phase cells, thenucleoid becomesconfined tothe center, andthisresults ina decrease inthedensity ofthis portion ofthecell(3,6,21). Recently there hasbeena resurgenceofinterest innucle- oidstructure. Inpart, this hasresulted fromthedevelopment ofcryofixation techniques forelectron microscopy (13), the availability ofDNA-specific fluorescent stains suchas4',6- diamidino-2-phenylindole

Mucociliary clearance of the respiratory tract is, besides cough, the principal mechanism to remove particles from the mucosal surface of bronchi and trachea. The mucosa is covered with a thin layer of mucus. Driven by the beating cilia of specialized epithelial cells, this thin mucous blanket is moved at a rate of 0.5 to 1.5 cm/min toward the larynx, where the mucus is either swallowed or expectorated.

Microbial Physiology Relations Between Structure and Function in the Prokaryotic Cell (Society for General Microbiology Symposium 28), edited by Stanier R. Y. Rogers H. J. Ward J. B.. Cambridge University Press, New York, 1978, 369 p., illus., $36.00. Lolita Daneo-Moore, Lolita Daneo-Moore Department of Microbiology & Immunology, Temple University, Philadelphia, PA 19140 Search for other works by this author on: Oxford Academic Google Scholar Michael L. Higgins Michael L. Higgins Department of Microbiology & Immunology, Temple University, Philadelphia, PA 19140 Search for other works by this author on: Oxford Academic Google Scholar BioScience, Volume 29, Issue 2, February 1979, Page 114, https://doi.org/10.2307/1307749 Published: 01 February 1979

(1971). Procaryotic Cell Division with Respect to Wall and Membranes. CRC Critical Reviews in Microbiology: Vol. 1, No. 1, pp. 29-72.