82 LIFE: ITS NATURE AND ORIGIN 



1) Develop at reactions close to neutrality (species Th. 



thioparus, Beijerinck) 



2) Develop under very acid conditions (species Th. thio- 



oxidans, Waksman and Joffe) 

 b) Anaerobic (species Th. denitrificans, Beijerinck) 

 (2) Facultative autotrophic 



a) Facultative anaerobic (species of Trautwein) 

 (b) Higher bacteria (complex in morphology) 



(1) Colorless (includes genera Beggiatoa, Thiothrix, Thioploca, 



Achromatium, Thiophysa, Thiovulum, and Thio- 

 spira) 



(2) Pigmented red or purple bacteria (over 16 genera) 



C. Bacteria which oxidize ferrous or manganeous compounds 



(a) Simple bacteria 



(1) Long excretion filaments (genus Gallionella) 



(2) Coccoid or oval shapes in masses (Siderocapsa, Sideromonas) 



(b) Filamentous bacteria (genera Leptothrix, Crenothrix) 



D. Bacteria which oxidize hydrogen. 



S. Winogradsky 2 pioneered in this field; first studying certain higher 

 sulfur bacteria, later iron bacteria and nitrifying organisms. The 

 latter convert urine, etc. into nitrates from which was made saltpeter, 

 a vital ingredient of gunpowder. 



All known living units appear to have the further power of un- 

 dergoing generally infrequent but marked deviations from their 

 usual composition, structure and function; and in some cases 

 these changes alter or modify their ability to direct catalytically 

 the formation and decomposition of various chemical substances, 

 and are, furthermore, passed on hereditarily when the living unit 

 reproduces itself by autocatalysis. 



Many geneticists have held, and a few may still believe, that all 

 heritable changes are due to abrupt changes in genes ("muta- 

 tions"). This notion was apparently supported by the pioneer 

 work of Professor Herman J. Muller (Nobel prize, 1946) and his 

 followers on the effects produced by subjecting to controlled x-ray 

 treatment eggs, sperms, and seeds. Later it appeared that they 

 might be caused by chromosomal rearrangements rather than 

 changes in gene structure. These matters are considered further 

 in Chapter 8. 



Increasing experimental evidence is being found for the view 

 that — apart from heritable changes in the genes and chromosomes, 

 admittedly the main carriers of heredity — the cytoplasm, that pool 

 of "protoplasm" with its numerous enzymic catalysts, mito- 



