PRINCIPLES OF BACTERIOLOGY 



Such bacteria as the pneumococcus, tubercle, influenza, diphtheria, 

 glanders, and leprosy bacilli do not develop, as far as we know, out- 

 side of the body under ordinary conditions. Under exceptional circum- 

 stances, as in milk, some may develop. Others, again, such as the 

 streptococcus and staphylococcus, typhoid and anthrax bacillus, the 

 cholera spirillum, and some anaerobics, may develop under peculiar 

 conditions existing in water or soil. 



While for the pathogenic bacteria, as a rule, the saprophytes met 

 with in the soil and water are antagonistic, yet in some cases and 

 especially is this true of the anaerobic bacteria they are helpful. 

 Such bacilli as tetanus are believed to require the association of 

 anaerobic bacteria to permit of their development in the soil in the 

 presence of oxygen. 



5. Ability to develop in or upon some portion of the skin or mucous 

 membrane, either after or before disease, and without causing infection. 

 As complete a knowledge as possible of this saprophytic development in 

 man of parasitic bacteria is necessary if we are to combat the spread 

 of infection. In the superficial layers of the epithelium and on the sur- 

 face of the skin we find the different pyogenic cocci, which are capable 

 of infecting a wounded or injured part or causing inflammation in the 

 glands. Acne, the pustules in smallpox, the pus on a burned surface, 

 boils, etc., all come from these pyogenic cocci. In surgical cases the 

 skin has to be as thoroughly disinfected as possible, to prevent the 

 formation of stitch-hole abscesses and wound suppuration. 



In the secretion of the mucous membrane covering the pharynx and 

 nasopharynx there is always an abundance of bacteria. In throats ex- 

 amined in New York City, streptococci, staphylococci, and pneumo- 

 cocci are found in almost every instance, and even in the country they 

 are often present. In the anterior nares there are fewer parasitic 

 bacteria than in the posterior portions. The nasal secretion is only 

 very slightly, if at all, bactericidal. Many other varieties of bacteria, 

 such as the meningococci and the influenza bacilli, are probably often 

 present in small numbers. In those constantly in contact with cases 

 of diphtheria, and in those convalescent from diphtheria, virulent 

 diphtheria bacilli are frequently found in the throat. 



After exposure to cold or injury of any kind, owing to the presence 

 of these bacteria, the persons harboring them may develop tonsillitis, 

 tonsillar abscess, or diphtheria; or the bacteria may invade the bron- 

 chial mucous membrane or the lungs. The diphtheria bacilli, and 

 perhaps other bacteria, transmitted to others may become the source 

 of infection to them, though the person who spreads the infection may 

 remain unaffected. 



After typhoid fever the bacilli may remain in the intestinal con- 

 tents for weeks and in the bladder and gall-bladder for months. 



Autoinfection. Some good observers have stated that bacteria can 

 be absorbed through the intestinal wall into the chyle and blood. 

 When the intestinal canal is injured, or its circulation hindered by 

 strangulation, etc., the bacillus coli and some other bacteria may 



