530 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



the nose or the mouth may either pass to the lungs through the 

 trachea or down the oesophagus to the stomach and intestines. Dur- 

 ing the ordinary inspiratory part of a respiration it is probable that 

 microorganisms cannot pass directly into the alveoli of the lung, as the 

 tortuous passage, the mucous and cilia are fairly efficient barriers. 

 Bacteria may be inhaled directly into the finer bronchi and the alveoli 

 during forced inspiration such as that attendant upon hiccoughing and 

 sneezing. Infections of this kind occur in pneumonia and influenza. 

 Microorganisms lodge on the membrane of the trachea and are carried 

 to the lungs and occasionally to other parts of the body by the blood 

 and lymph. It is probable that such a form of infection occurs some- 

 times in pneumonia, tuberculosis and the plague. 



Infectious microorganisms very frequently pass down to the stomach 

 and intestines. The mucous membrane of the stomach is normally 

 very resistant to infection due to the hydrochloric acid which is present 

 in the gastric juice and which in normal amount is distinctly antiseptic. 

 In instances where the acidity of the stomach is lowered microorganisms 

 will develop more readily. Toxins with the exception of that of B. 

 botulinus, of meat poisoning, are destroyed by the gastric juice. The 

 intestines are less resistant to infection. It is here that the causal 

 microorganisms of typhoid fever, Asiatic cholera, chicken cholera and 

 dysentery and the various hemorrhagic septicaemias find their partic- 

 ular affinities. These bacteria enter or attach themselves to the intestinal 

 wall and, in the case of cholera and dysentery, this is the only point of 

 infection. The B. typhosus has occasionally been known to enter at other 

 places. This bacterium, however, commonly localizes in the lymphatic 

 patches (Peyers) of the intestine. Some bacteria can pass through the 

 wall of the intestine when it is seemingly intact. This point has been 

 repeatedly demonstrated in the case of Bad. tuberculosis. 



The genital organs of the male and female are susceptible to infection 

 with microorganisms in certain instances. The M. gonorrhoea, of gon- 

 orrhoea, and the Treponema pallidum, of syphilis, find their usual portals 

 of entry, in the genital tract. They have, however, been known to infect 

 other parts of the body as the mouth, skin and the conjunctiva. Other 

 bacteria, as for example, the Strept. pyogenes, M. pyogenes var. aureus 

 and B. coli are sometimes found infecting the genital tract in cases of 

 chronic urethritis. 



The kidneys, ureters and bladder are sometimes infected but usually 



