56 Causes of Disease. 



blood and internal organs only after death of the animal (mostly 

 putrefactive organisms). 



Those parts of the human or animal body which are freely 

 accessible are exposed to the entrance of bacteria as of anything 

 else from the exterior. Many of these microorganisms find fa- 

 vorable conditions for existence in the surface of the skin and 

 mucous membranes, live and multiply there without doing harm, 

 finding their nutrition in the secretions and refuse of such lo- 

 calities. They come from the air where they exist in the dust, 

 from food and drink, and, in fact, from any objects in which 

 they exist and with which contact is had. In our alimentary 

 tracts there are always millions of bacteria* and other fungi, in 

 the stomachs of ruminants countless infusoria, all of which par- 

 take of the nutrient fluid and aid by certain secretions of their 

 own in the digestion of the food, but have no pathogenic action ; 

 they are our table guests (commensualists) and stand in a re- 

 lation of symbiosis to us (living together for mutual profit). 

 As long as these conditions are maintained and as long as they 

 obtain their nutrition merely from the dead material they may 

 be considered as harmless saprophytes {(rairpbs, decayed; (pijrov, 

 vegetable growth). Their harmlessness is explicable by the fact 

 that these microorganisms are not in any way fitted for attack- 

 ing the living substance of the animal body, and their metabolism 

 gives rise to no products which might be toxic to the cells and 

 tissues of the animal ; or whatever toxines there may be are 

 quickly neutralized by the body secretions. Besides, their increase 

 is held in check by the various adjustment powers of the body. 

 The protective epithelium of the skin and mucous membranes 

 prevents their penetration into the tissues ; they are expelled 

 from the air passages by the activity of the cilia of the lining 

 epithelium and from time to time by the expectoration of mucus ; 

 many are retarded in their growth by the acidity of the gastric 

 juice and by the intestinal secretions, as well as by the bile; 

 large numbers are expelled with the excrement from the in- 

 testines ; many dry up upon the surface of the body. Moreover, 

 the various organs and cells, as the liver and phagoc3^tes and the 

 blood particularly, contain substances of antitoxic and microbici- 



•A stained smear preparation should be made from the surface of the gums, 

 tongue or throat of a convenient cadaver as proof of the interesting flora existing 

 there and as evidence of the wandering corpuscles in our cellular constitution. Vld. 

 for fuller consideration Kitt, Bakterienkunde f. Tierdrztc, IV. Aufl. Wien, 1903 



