130 BACTERIOLOGY. 



causing infection. As complete a knowledge of these 

 facts as possible is necessary if we are to combat the 

 spread of infection. In the superficial layers of the 

 epithelium and on the surface 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 the 

 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- suppura- 

 tion. 



In the secretion of the mucous membrane covering 

 the pharynx and nasopharynx there is always an abund- 

 ance of bacteria. In one hundred throats examined by 

 the writer in New York City, streptococci and staphylo- 

 cocci could be found in over 90 per cent., and pneumo- 

 cocci were very frequently discovered. Many other 

 varieties of bacteria, such as the influenza bacilli, are 

 probably often present in small numbers. In those con- 

 stantly 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 diph- 

 theria; or the bacteria may invade the bronchial mucous 

 membrane or the lungs. The diphtheria bacilli, and 

 perhaps other bacteria, transmitted to others may be- 

 come the source of infection to them, though the person 

 who spreads the infection may remain unaffected. 



The stomach, on account of the acidity of its con- 

 tents, is'Vomparatively free from bacteria. The normal 



