ENTRANCE AND SPREAD OF BACTERIA. 



181 



normal conditions. The pneumococcus of Fraenkel and 

 the pneumobacillus of Friedlander have also been found in 

 the mouth and in the nasal cavity in normal conditions, 

 whilst the bacillus coli communis is a normal inhabitant ot 

 the intestinal tract The entrance of these organisms into 

 the deeper tissues when a surface lesion occurs can be 



FJG. 51. Minute focus of commencing suppuration in brain case of 

 acute ulcerative endocarditis. In the centre a small haemorrhage ; to 

 right side dark masses of staphylococci ; zone of leucocytes at periphery. 



Alum carmine and Gram. x 50. 



readily understood. Their action will, of course, be 

 favoured by any depressed condition of vitality. Though 

 in normal conditions the blood is bacterium-free, we must 

 suppose that from time to time a certain number of such 

 organisms gain entrance to it from trifling lesions of 

 the skin or mucous surfaces, the possibilities of entrance 



