

BACTERIA. 33 



estimation. This is the micro-millimeter (/i), or one- 

 thousandth part of a millimeter, and about equivalent 

 to the one-twenty-five-thousaudth of an inch. 



As a rule, the spherical organisms are the smallest and 

 the spiral organisms the longest, except the chains of 

 bacilli called leptothrix. Their measurements vary from 

 0.15 fi (micrococcus of progressive abscess-formation in 

 rabbits) to 2.8 fx (Diplococcus albicans amplus) for cocci, 

 and from 1 X 0.2 ti (bacillus of mouse-septicemia) to 

 5 X 1.5 li (anthrax bacillus) for bacilli. Some of the 

 spirilla are very long, that of relapsing fever measuring 

 40 it at times. 



This estimation of size almost prepares one for the 

 estimation of weight given by Nageli, who found that 

 an average bacterium under ordinary conditions weighed 

 10000000000 of a milligram. 



The bacteria multiply by binary division (fission). The 

 bacterium which is about to divide appears a little larger 

 than normal, and, if a spherical organism, more or less 

 ovoid. No karyokinetic changes have been observed in 

 the nuclei, though they may occur. When the conditions 

 of nutrition are good, fission progresses with astonishing 

 rapidity. Buchner and others have determined the length 

 of a generation to be from fifteen to forty minutes. 



The results of binary division, if rapidly repeated, are 

 almost appalling. " Cohn calculated that a single germ 

 could produce by simple fission two of its kind in an 

 hour ; in the second hour these would be multiplied to 

 four ; and in three days they would, if their surroundings 

 were ideally favorable, form a mass which can scarcely be 

 reckoned in numbers, or, if reckoned, could scarcely be 

 imagined — four thousand seven hundred and seventy-two 

 billions. If we reduce this number to weight, we find 

 that the mass arising from this single germ would in 

 three days weigh no less than seventy-five hundred 

 tons." "Fortunately for us," says Woodhead, "they 

 can seldom get food enough to carry on this appalling 

 rate of development, and a great number die both for 

 3 



