ANTISEPTICS 509 



means of gaseous disinfection. (See p. 255.) In most barns gaseous dis- 

 infection is useless because the premises cannot be made air-tight. 



ANTISEPTICS. 



It is perhaps well to consider here the sources of infection and the 

 natural defenses or immunity possessed by animals against parasitic in- 

 vasion. Pathogenic micro-organisms are commonly brought in contact 

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

 and insects (flieSj ticks, lice, and mosquitoes), and gain entrance by means 

 of the air passages, digestive canal and blood j 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 respiratory tract. But when the mucous mem- 

 brane is damaged by inflammation, and the ciliae become 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* acts as a natural 

 antiseptic, while the liver is thought to destroy toxins resulting from 

 bacterial life. 



When digestion is in a normal condition, putrefaction and fermenta- 

 tion do not occur; but when its activity is diminished, and the secretion 

 of the digestive juices is lessened, and the hepatic functions are de- 

 pressed, 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 outlying pickets shielding the animal from bacterial 

 invasion, we must add the intrinsic power of resistance vested in the 

 tissues, blood serum (opsinins, bacteriolysins, agglutinins), and leukocytes 

 in combating niicro-organisms ; and the production of antibodies in the 

 system antagonizing the toxins formed by bacterial action. Micro-organ- 

 isms are always to be found on the surface of the body and within its 

 natural cavities open to the air, but pathogenic bacteria are less likely 

 to do harm if the animal is in a healthy condition. A limited number of 

 bacteria (micrococci) may even exist within the blood in health, and this 

 fact accounts for suppuration occurring when the tissues are severely 

 injured, without solution of continuity. The internal use of antiseptics 

 is of comparatively little value, even when these agents come in direct 

 contact with germs in -the digestive tract. This follows because it is im- 

 possible to administer antiseptics in sufficient amount to seriously inter- 

 fere with bacterial growth in the tissues, without injuring or even killing 

 the patient. 



There are certainly known but two instances (quinine in malaria and 

 salvarsan in syphilis) where the exhibition of an antiseptic will inhibit 

 the development of micro-organisms of a general infectious disease, and 

 so absolutely arrest it. It is probable, however, that salicylates in rheu- 

 matism, act therapeutically as internal antiseptics. Antiseptics are of 

 benefit in rendering the contents of the digestive tube more or less aseptic, 



•Experiments In human patients show that many forms of pathogenic bac- 

 teria may live in bUe. It is but moderately bactericidal. 



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