696 A MANUAL OF BACTERIOLOGY 



Mouth. Micro-organisms of all kinds are present in the buccal 

 cavity in the greatest abundance leptothrix, bacilli, pyogenic 

 cocci, Sarcinae, and spirilla are almost always to be found. The 

 Streptococcus pyogenes, M. pyogenes, var. aureus, and Streptococcus 

 pneumonice are frequently present. Certain organisms have their 

 normal habitat in the mouth, are difficult to cultivate, and are of 

 considerable importance in the production of dental caries. 1 

 Well-defined micrococci and streptococci also occur in the saliva 

 (M. salivarius, p. 274, and 8. salivarius, p. 279). The normal 

 saliva is germicidal to some extent. (See also p. 556.) 



Stomach and intestine. Although a vast number of organisms 

 gain access to the stomach, a large number are destroyed by the 

 acid gastric juice. At the same time a considerable proportion 

 are able to survive sarcinse, and lactic and butyric acid bacilli. 

 In normal nurslings the mouth and stomach contain few bacteria 

 a few cocci, and some bacilli of the B. coli and B. lactis aerogenes 

 groups. The small intestine contains organisms of the same 

 types, but scantily. In the large intestine bacteria are extremely 

 numerous, particularly Gram-positive ones. These are mostly 

 slender, slightly curved bacilli of moderate size, the B. bifidus of 

 Tissier, which often has a bifid extremity, also a somewhat similar 

 organism, B. acidophilus of Moro, but capable of developing in an 

 acid medium, a few B. Welchii, and a diplococcus. The Gram- 

 negative forms are B. coli, B. lactis aerogenes, and cocci. In bottle- 

 fed children the same organisms occur, but the preponderating 

 organisms are Gram-negative of the B. coli type, with many cocci 

 and streptococci. In childhood and adolescence organisms of the 

 bifidus type become less numerous but putrefactive anaerobes 

 become more so, particularly B. Welchii and B. putrificus (coli) of 

 Bienstock ; the latter is a long, slender, Gram -positive bacillus 

 with large terminal spores. During adult life the putrefactive 

 anaerobes tend to become still more numerous, and the putrefac- 

 tive decompositions they produce were regarded by Metchnikoif 

 as standing in causal relation to old age. In the healthy adult 

 the stomach, duodenum and jejunum contain relatively few 

 organisms, from the lower ileum to the rectum the intestinal 

 contents are crowded with bacteria, and the greatest number of 

 anaerobic organisms occur here and putrefactive changes are 



1 See Goad by, Mycology of the Mouth. 



