BACTERIOLOGY. 149 



CHAPTER XXIV. 



SIZE, NUMBERS, AND DISTRIBUTION. 



Size and numbers. The unit of measurement for bacteria is 

 the micromillimeter, which is the thousandth part of a millimeter. 

 It is represented by the Greek letter /*. The size of Bacillus tuber- 

 culosis is: Length, 1.5/ji to 4,u; diameter, 0.2,u to 0.5, a. Some 

 cocci are as small as 0.1 5 /A in diameter; others as large as 2.8^i 

 in diameter. Bacilli range from lxO.2// to 5xl.5,u. Some spirilla 

 are40/jt long. The number of known species is upward of 1,000 

 The individuals of any species are countless. Dr. Sternberg states 

 that a milligram of the pure culture of StapJiylococcus pyogenes 

 aureus contains 8,000,000,000 individuals. The weight of an av- 

 erage bacterium has been estimated by Nageli to be 1-10,000,000,000 

 milligram. 



The following estimates, as given by Williams, will give some 

 conception as to the number of bacteria that form a part of the in- 

 visible world of teeming organisms. The number of individuals in 

 1 c. c. of virgin soil is estimated to be upward of 100,000. Ordinary 

 milk contains more than 20,000 to 1 c. c. The number of bacteria 

 in a milligram of human fecal matter will range from 70,000 to 

 33,000,000. 



Distribution. The estimates just given will suggest that bacteria 

 are very widely distributed. Their spores float upon the dust of the 

 atmosphere in untold millions ; they swarm in the water we drink : 

 they teem in the soil to the depth of three feet ; they abound in food 

 and in all decaying substances; and they take up their abode in 

 the human body, being present in the alimentary tract in large 

 numbers, except in new-born infants. It is believed that the air 

 upon the high seas and upon mountain tops, the deeper layers of the 

 soil, the water of uncontaminated springs, and tfye tissues and fluids 

 of the normal body which are not exposed to the external atmos- 

 phere are free from their presence. 



The presence of bacteria in soil, air, water, milk, blood, urine, 

 and fecal matter may be demonstrated by making plate cultures 



