ABILITY OF BACTERIA TO PRODUCE DISEASE 97 



sores develop on the teeth and lips as a result of bacterial 

 growth. 



The gastric juice through the hydrochloric acid it contains has 

 a marked germicidal effect. Nevertheless, many bacteria escape 

 its action because they are protected in the food or because of its 

 neutralization. Bacteria causing typhoid fever, cholera, tuber- 

 culosis, and other infections may thus pass unharmed into the 

 intestines and there produce their respective lesions. 



Most inhaled organisms which pass the larynx are gradually re- 

 moved by the ciliated epithelium of the bronchi ; the few which 

 succeed in gaining entrance to the lungs are able to multiply and 

 produce disease only when the lung tissues have lost some of their 

 resistant powers. 



Points of Entrance. Infection occurs with certain bacteria 

 only when they enter the body by an appropriate route and reach 

 special tissues. Thus typhoid, cholera, and dysentery infection 

 does not take place unless the organisms enter the gastro-intestinal 

 tract ; they never enter through the skin. Gonococci usually enter 

 the body through the genital organs or occasionally the eye, but 

 never by way of the respiratory or digestive tract. The avenue 

 of invasion thus determines largely whether infection will or will 

 not occur, and if it does its nature and severity. Diphtheria 

 bacilli rubbed on an abrasion of the hand produces only a slight 

 lesion, but rubbed on an abrasion of the throat they cause inflamma- 

 tion, necrosis of the tissue, and a general poisoning. Pneumococci 

 lodging on the surface of the eye may cause a severe conjunctivitis, 

 on the mucous membrane of the throat a pseudomembranous 

 angina, and in the lungs pneumonia. 



Several species of bacteria are normally present in the mouth, 

 some of which may be the cause of caries of the teeth. The im- 

 portance of this condition is becoming more and more recognized 

 as having a direct bearing on the general health. A carious tooth 

 may be the portal of entrance for microorganisms causing a gen- 

 eral infection. 



The mode of entrance of the tubercle bacilli is still a disputed 

 point. The theory that they enter through the respiratory tract 



