72 BACTERIOLOGY 



abnormal circumstances come to produce disease. Bacillus coli, 

 however, is usually by far the most numerous of these. If, 

 from damage to the wall of the intestine, either from actual 

 wounds or from disease, B. coli is enabled to make its way into 

 the ^tissues, it may give rise to serious disease, abscesses, peri- 

 tonitis, appendicitis, or the like being very commonly due to 

 this organism, either alone or in company with other bacteria. 

 Primary infection in these parts by the latter, e.g. by Strepto- 

 or Pneumococci, etc., is frequently complicated by the secon- 

 dary appearance of B. coli in the lesion, and the latter organism 

 may then outgrow and obscure the original cause. Infection 

 of the urinary tract with B. coli is very common, especially in 

 women and children ; whilst this organism, as previously men- 

 tioned (p. 58), may also play a part in ordinary wound infec- 

 tion. Certain diseases of plants are believed to be caused by 

 an organism apparently identical with B. coli. 



B. coliia usually, though not under all circumstances, a motile 

 organism ; whilst certain very closely allied bacilli, known as the 

 Capsulated Group, are non-motile, and, as their name implies, 

 possess a capsule around them. Some of these are very common 

 in sour milk, e.g. B. lactis aerogenes, which is usually non- 

 pathogenic. Bacillus pneumoniae or Friedlander's Pneumo- 

 bacillus, is very frequently found in nasal catarrh, sore 

 throats, bronchitis cases, and the like. It may also be found in 

 the lungs, in empyema pus, and in abscesses. Although it may 

 itself cause disease, it is more usually associated with or follows 

 invasion by other pathogenic bacteria, such as Pneumo- or 

 Streptococci. It causes a rapidly fatal septicaemia if inoculated 

 into mice ; and on culture, it often gives a peculiar translucent 

 slimy or mucous growth which is more or less characteristic. 



losarceae : B. enteritidis of Gaertner and various Para- 

 typhoid bacilli and their relatives are of great importance in 

 connection with certain cases and epidemics of food-poisoning 

 which have already been discussed under that heading (pp. 41, 

 51). 



Typheae : B. Typhosus, the specific cause of Typhoid or 

 Enteric Fever, is a very important member of the Coli-Typhoid 

 group. It is actively motile, grows easily on most culture- 

 media, and is differentiated by numerous complicated special 

 cultural and other tests, of which the agglutination reaction, 

 often referred to in this connection as the " Widal reaction," 

 is the most useful (see p. 49). It does not curdle milk, and 

 may therefore be readily spread by means of it. Other impor- 

 tant facts in relation to its epidemiology, e.g. the carrier ques- 

 tion, have already been mentioned in a previous chapter (p. 55). 



