64 THE RELATION OF BACTERIA TO DISEASE 



in their course past the primary defences and their 

 manner of awakening the secondary or peculiar 

 immunity resistances which the human system pre- 

 sents. Bacteria gain entrance to the body by 

 introduction through an abraded surface of the skin 

 or mucous membranes. The delicacy of the latter 

 renders infection through them quite easy. They 

 may go in through the intestinal tract and be absorbed 

 by its wall. They may go in through the tonsils, 

 larynx, or trachea. In exposure to cold with the 

 congestion and sensitiveness of the larynx produced 

 thereby we have an opportunity for the absorption of 

 bacteria. Not all bacteria can enter by all ways and 

 produce disease. The pus cocci, if swallowed, are 

 destroyed by the gastric juice, while typhoid bacilli 

 usually pass the stomach uninjured. Typhoid bacilli 

 rubbed into the skin would be followed by no disease, 

 but pus cocci so applied would cause boils. Most of 

 the secretions and excretions, except, of course, the 

 feces, may be said to be mildly inhibitive to bacterial 

 growth. The defences of the body to a local introduc- 

 tion of bacteria depend upon the healthiness of the 

 skin and mucous membranes. The resistance offered 

 has been found to be due to a power supplied by the 

 blood serum. This is discussed later. Any physical 

 condition such as a burn or wound reducing the healthy 

 trim of the body renders invasion easier. Injury and 

 intoxication materially favor the activity of bacteria 

 either previously within the individual or introduced 

 at the time. Normal bodily resistance is impaired by 

 excessive hunger and thirst, by exposure to cold and 

 wet, or by prolonged muscular or mental strains. 



