CHAPTER VII* 

 MICROORGANISMS OF THE DIGESTIVE TRACT 



INTRODUCTION 



The digestive tube of the vertebrate animal is in communication 

 with the external world and is the passageway for a great variety of 

 materials constituting the food of the animal. This food brings with 

 it various sorts of microbes, at times in considerable numbers. Within 

 the digestive tube the food is more or less completely resolved by the 

 processes of digestion into soluble nutritive split products, which furnish 

 an excellent medium for microbic development. It is not surprising, 

 therefore, that there is an enormous multiplication of microorganisms 

 within the intestine, both in health and disease, and that this multi- 

 plication is most active during the digestion of the food. 



MICROORGANISMS OF CERTAIN PORTIONS OF THE ALIMENTARY CANAL 



The entire digestive tract is free from microbes during normal 

 intrauterine life. After birth the canal is quickly invaded by bacteria, 

 chiefly through the mouth and nose, but to a lesser extent also through 

 the anal orifice. In the mouth, pharynx and intestine, some of these 

 invaders establish themselves to remain throughout the life of the 

 individual host. The species of microbes present and the numerical 

 proportions of the different species of normal buccal and intestinal 

 microorganisms vary somewhat with the age of the host and the charac- 

 ter of his food. They are also considerably disturbed sometimes by 

 the entrance and multiplication of pathogenic germs, giving rise to 

 disease in their host, such as Oidium albicans in the mouth or the chol- 

 era vibrio in the intestine. 



MICROORGANISMS OF THE MOUTH. The buccal cavity presents 

 conditions of temperature, moisture, chemical reaction and a variety 

 of food substances in its various parts, which are very favorable to the 

 growth of many microbic species. Aerobic, facultative and anaerobic 

 forms are found and the species are very numerous. Miller, in a few 



* Prepared by W. J. MacNeal. 



38 593 



