Intermediate Organisms 191 



BACTERIA 



It is common to hear discussions regarding germs of various kinds. 

 Such discussions usually pertain to all those plants and animals which 

 are likely to cause disease. Bacteria, however, refer to very minute 

 plant organisms classified under the chlorophyl-less fungi (mycetes), 

 under the general grouping of schizomycetes ( ). 



While most diseases are probably due to, or associated with, bac- 

 teria, very few bacteria, relatively speaking, cause disease. The great 

 majority of them are of undoubted value to other' living organisms. 



There are three general shapes after which bacteria are named. The 

 bacillus is rod-shaped (b, f, k, 1, Fig. 88), the coccus (c, d, e, f, h, Fig. 

 88), (sometimes micrococcus), is berry-shaped or spherical, and the 

 spirillum is spiral-shaped or merely curved, something like a comma 

 (A, Fig. 88). Bacteria may be so small that only many thousands 

 together form a spot sufficiently large to be seen under a high power 

 microscope, or they may be of relatively large size. That is, they vary 

 from less than 1 micron (the measurement used in microscopy, meaning 

 1-1000 of a millimeter, or 1-25000 part of an inch) to 30 or 40 microns. 

 It has been estimated (Migula) that there are 1272 distinct species of 

 bacteria. 



Not only do bacteria vary according to shape, but as to their method 

 of growth under varying conditions of temperature and surrounding 

 substance. 



Bacteria may possess cilia or flagella and move quite rapidly. They 

 reproduce by simple binary fission. The spirillum and bacillus divide at 

 right angles, usually lengthening slightly before division. Cocci may 

 divide in different planes, and various names have been assigned to them 

 on this account. If they divide into two parts but remain attached, they 

 are called diplococci ( ). If they continue dividing 



in one plane but remain attached so as to form chains, they are called 

 streptococci ( ). If they divide in two planes. 



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Fig. 89. Various Groupings of Spherical Forms of Bacteria. 



a, Tendency to lancet-shape; b, coffee-bean shape; c, in packets (sar- 

 cina) ; d, in tetrads; e, in chains (streptococcus); /, in irregular masses 

 (staphylococcus). Magnified 1000 diameters. (After Fliigge.) 



