DIVISION II 



BACTERIA, SCHIZOMYCETES 



18. 31-39 



(p..3) 



Bacteria are extremely minute, unicellular organisms, which in 

 outline present three primary forms each of great simplicity, 

 namely the spheres (cocci), ^ 



the straight rods (bacteria), 

 the curved rods (splrilli). 



In addition to these forms 

 which comprise the vast 

 majority of known species 

 of bacteria there are also 

 bacteria consisting of fila^ 

 mentous bodies, either sim- 

 ple or branched, attached or free 



Fio. 4. — The three type forms of bacteria; 

 a, spheres; b, rods; c, spirals. After Conn. 



In both structure and phys- 

 iology bacteria are allied to the vegetable kingdom and in it 

 most closely to the blue green algae. 



Bacteria are inconceivably small. Most of the spherical bacteria 

 fall within the limits of from 0.5 to 1.5 n in diameter. Among 

 the rod and curved bacteria the length in most species is between 

 1 and 1.5 /x, the diameter between 0.5 and 1 n. Among the 

 largest species is B. megatherium, 2.5 x 10 >i; Clostridium butyri- 

 cum, 3 X 10 /*; and Spirillum volutans, 13 to 50 /* long. Among 

 the smallest is Spirillmn parvum 0.1-0.3 /i in diameter and Pseudo- 

 monas indigofera 0.06 x 0.18 ii. 



It is practically impossible to conceive these dimensions. An 



illustration may aid the imagination. The paper on which these 



words are printed is about 87.5 /* thick. It 



• would therefore take about 200 bacteria of ordi- 



Fio. 5.— This dot is nary size or 400 moderately small or 20 very 



1 mm. in diameter. ^^^^^ ^^^ placed end to end to equal in length 



the thickness of this paper. It would take 1571 ordinary bacteria 



(1 X 2 /i) end to end to reach around the circumference of a dot 



13 



