150 PRINCIPLES OF BACTERIOLOGY 



bactericidal saliva. When the teeth are decayed many varieties of 

 bacteria abound. The bacteria, such as the diphtheria bacilli, strepto- 

 cocci, etc., rarely invade the mucous membrane of the tongue or mouth. 



The tonsils with their crypts are usually the seat of the pyogenic 

 cocci and are readily infected by the diphtheria bacilli and others. 

 Whether the absolutely intact epithelium allows the passage of these 

 bacteria is disputed, but with the slight pathological lesions usually 

 present it undoubtedly does. 



THE LUNGS. Most inhaled bacteria which pass the larynx are 

 caught in the bronchi. Many of these are gradually removed by the 

 ciliated epithelium. Both the alveolar epithelial cells and the leukocytes 

 which enter the air sacs and bronchioles have been shown to take up 

 bacteria. The normal lung is, therefore, rapidly freed of bacteria. 

 Under the influences of certain nervous impressions such as follow 

 exposure to cold, etc., certain areas of the lung seem to lose their 

 protective defences. 



THE STOMACH. The pure gastric juice, through the hydrochloric 

 acid it contains, is able to kill most non-spore-bearing organisms in a 

 short time, but because of neutralization through food, or because the 

 bacteria are protected in the food, many of them pass into the intestines. 

 Tubercle, typhoid, colon, and dysentery bacilli, when fed by the mouth 

 with food, readily pass through the stomach. Certain acidiphilic germs, 

 as well as yeasts and torulse, seem to grow in the gastric secretion; these 

 are largely non-pathogenic. Perforation of the stomach is usually 

 followed by peritonitis, because of the irritant effect of the gastric juice 

 and the presence of bacteria which are temporarily retained. The 

 gastric juice neutralizes tetanus and diphtheria toxins. Other poisons, 

 such as some that occur in decayed meat, are not neutralized. The 

 stomach is exceptionally free from bacterial inflammations. 



INTESTINES. The bile is feebly bactericidal for some bacteria, but, 

 on the whole, the intestinal secretions have little or no germicidal power. 

 The number of bacteria increase steadily from the duodenum to the 

 head of the colon, and diminish slightly from the upper to the lower 

 end of the colon. The pancreatic juice destroys many of the toxic 

 bacterial products. The presence of the bacilli of the colon group, of 

 streptococci, etc., do not often set up any inflammatory condition in the 

 normal intestines of healthy persons. In children suffering from the 

 prostrating effects of heat they are apt to excite inflammatory changes. 

 Even pathogenic bacteria, such as the typhoid, dysentery, and tubercle 

 bacilli, may pass through the whole length of the healthy intestines 

 without inciting inflammations. Slight lesions aid the passage of bacteria 

 to the deeper structures. 



Importance of Location of Point of Entry of Bacteria. Most bacteria 

 cause infection only when they gain access to special tissues and must, 

 therefore, enter through certain portals. This fact is of immense impor- 

 tance in the transmission or prevention of disease. Thus, for example, 

 let us rub very virulent streptococci, typhoid bacilli, and diphtheria 

 bacilli into an abrasion on the hand. The typhoid bacillus produces no 



