THE BACTEKIA (SCHIZOMYCETES) 163 



149. Size. The variations in size are even greater than 

 those in form. The average bacillus type of bacterium is about 



?5 <Jo o mch Ci (To o mm O in diameter and T ^ Q o inch (4^0 mm O 

 in length. The spherical bacteria have an average diameter 

 slightly less than that of the average bacillus forms, while 

 most spiral forms are larger. There are known forms that are 

 very much smaller than these averages. It is indeed thought 

 by some bacteriologists that the failure to discover the bacteria 

 that produce certain diseases is due to our inability, even by 

 means of the most powerful microscopes, to see these organ- 

 isms. It is suggestive in this connection to state that the 

 organism which produces yellow fever (perhaps an animal 

 organism and not a bacterium at all) is small enough to pass 

 through the pores of a compact porcelain filter. 1 



If the average bacteria are ^-g- o~o inch in diameter and y-Q J^-Q 

 inch in length, and if such bacteria were placed upon one 

 another end to end compactly until a pile one inch long, one 

 inch high, and one inch wide was constructed, the cubic-inch 

 mass would contain 6,250,000,000,000 individual bacteria. 

 This is approximately 65,000 times the number of human be- 

 ings in the United States. Or, assuming that a man's finger 

 nail is -$ inch (J- mm.) in thickness, by placing one upon an- 

 other, end to end, to make a single stack of average bacteria 

 as high as the finger nail is thick would require no less than 

 200 bacteria. 



150. Structure. These are extremely simple plants, and are 

 believed by some to be structurally the simplest known living 

 things. The wall of the cell is often made up of a slime-like 

 sheath. In some bacteria this wall is a distinctly gelatinous 

 capsule. It is not of cellulose material, as it is in the higher 

 plants. Internally the cell structure is quite simple, consisting 

 of structures that are thought to be cytoplasm and granules 

 of nucleus-like material. 



Many bacteria have been observed to have long hair-like 

 flagella extending from or through the cell wall (Fig. 150). 

 1 Reed and Carroll, American Medicine, 1902, p. 301. 



