DISINFECTANTS, ANTISEPTICS AND DEODORANTS 723 



ANTISEPTICS. 



It is perhaps well to consider here the sources of 

 infection and the natural defenses or immunity possessed 

 by animals against parasitic invasion. Pathogenic micro- 

 organisms are commonly brought in contact with the body 

 through the agency of the air, drinking water and food, and 

 insects (flies and mosquitoes), and gain entrance by means 

 of the air passages, digestive canal and blood ; but even in the 

 two former cases, the micro-organisms are in a certain sense 

 outside of the body, since it is not easy for them to penetrate 

 the intact and healthy ciliated mucous membrane of the re- 

 spiratory tract. But when the mucous membrane is damaged 

 by inflammation, and the cilise becomes paralyzed, and 

 abnormal secretions are formed, then a favorable opportunity 

 is offered for their growth and entrance into the circulation. 

 In the digestive tract the hydrochloric acid of the gastric 

 juice and bile* act as natural antiseptics, while the liver is 

 thought to destroy toxins resulting from bacterial life. 



When digestion is in a normal condition, putrefaction 

 and fermentation do not occur; but when its activity is 

 diminished, and the secretion of the digestive juices is 

 lessened, and the hepatic functions are depressed, then a 

 chance is offered for bacterial growth, fermentation and 

 absorption of toxins, or even actual transmigration of 

 micro-organisms through the intestinal walls. To these 

 natural agencies of defense, which may be likened to out- 

 lying pickets shielding the animal from bacterial invasion, 

 we must add the intrinsic power of resistance vested in the tis- 

 sues, blood serum (opsinins) and leucocytes in combating mi- 

 cro-organisms ; and the production of antitoxins in the body, 

 antagonizing the toxins formed by bacterial action. Micro- 

 organisms are always to be found on the surface of the body 

 and within its natural cavities open to the air, but patho- 



* Recent experiments in human patients show that many forms of 

 pathogenic bacteria may live in bile. It is but moderately bactericidal. 



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