1 62 MANUAL OF BACTERIOLOGY. 



casionally the exanthematous fevers are transmitted from 

 the mother to the fetus. 



The surfaces covered with thick stratified epithelium are 

 not likely to be penetrated by bacteria excepting by direct 

 introduction through some wound or other lesion. This, 

 for instance, is true of the skin, the mouth, the vagina and 

 bladder. The infection of bubonic plague appears to be 

 introduced most often by means of wounds in the skin. 

 Bacteria more easily penetrate surfaces having a thin 

 columnar epithelium such as occurs in the intestines, the 

 middle ear, bronchi and bronchial tubes, uterus and Fallo- 

 pian tubes. 



The thin, flat epithelial cells of the air-vesicles of the 

 lungs, as would be expected, seem to be passed with com- 

 parative ease. On epithelial surfaces covered with cilia, 

 as in the bronchi and bronchial tubes, the Eustachian tubes, 

 the uterus and Fallopian tubes, the current toward the ex- 

 terior created by the cilia acts beneficially in removing 

 bacteria. 



The tonsils and lymph-follicles of the intestines, espe- 

 cially the lymphoid tissue of the ileum and the vermiform 

 appendix, are points where bacterial invasion frequently 

 begins. The lymphoid tissue of the appendix may have 

 some influence in predisposing to infection at that point 

 and to appendicitis. On the other hand, it is certain that 

 the progress of many infections is checked by the lymph- 

 nodes. That is repeatedly seen in the ordinary post-mor- 

 tem wound where the spread of the inflammation along the 

 arm is checked suddenly at the elbow or axilla. The par- 

 ticipation of the lymphoid structures in most infections is 

 well known. How far this is a conservative process it is 

 impossible to say. 



In most cases of infectious disease a point of entrance 

 for the bacteria may be discovered. As a rule, the invading 



