CHAPTER II. 



BIOLOGY OF BACTERIA. 



THE distribution of bacteria is well-nigh universal. 

 They and their spores float in the atmosphere we breathe, 

 swim in the water we drink, grow upon the food we eat, 

 and luxuriate in the soil beneath our feet. Nor is this 

 all, for, entering the palpebral fissures, they develop upon 

 the conjunctiva; entering the nares, they establish them- 

 selves in the nose; the mouth is always replete with them; 

 and, as many are swallowed, the digestive apparatus always 

 contains them. The surface of the body never escapes 

 them, and so deeply are some individuals situated among 

 the epithelial cells of the skin that the most careful washing 

 and scrubbing and the use of the most powerful germicides 

 are required to rid the surgeon's hands of what may prove 

 to be dangerous hindrances to the healing of wounds. The 

 ear is not without its microscopic flora; special varieties 

 live beneath the finger-nails, and especially the toe-nails, 

 in the vagina, and beneath the prepuce. 



They are not, however, ubiquitous, and Tyndall* suc- 

 ceeded in proving that the atmosphere of high Alpine alti- 

 tudes was free from them, and likewise that the glacier 

 ice contained none; but wherever man, animals, or even 

 plants, live, die, and decompose, bacteria are sure to be 

 present. 



Notwithstanding their intimate relationship with the 

 animal body, the body-juices and tissues of normal animals 

 are free from them, and their occasional occurrence there may 

 be accepted as a sign of disease. 



The presence of bacteria in the air generally depends 

 upon their previous existence in the soil, its pulverization 

 and distribution by currents of the atmosphere. Koch 

 has shown that the upper stratum of the soil is exceedingly 

 rich in bacteria, but that their numbers decrease as the soil 

 is penetrated, until below a depth of one meter there are 

 very few. Remembering that bacteria live chiefly upon 



* "Floating Matter in the Air." 

 38 



