CHAPTER V. 



SAPROPHYTISM, PARASITISM, AND PATHOGENISM. 



I. DEFINITIONS AND LIMITS. 

 II. THE CYCLE OF PARASITISM. 



III. THE CYCLE OF PATHOGENISM. 



IV. DISTRIBUTION OF PARASITIC AND 



PATHOGENIC BACTERIA IN NA- 

 TURE. 



V. How PARASITIC AND PATHOGENIC 

 BACTERIA REACH MAN. 



A. The Occurrence of Parasitic 



Bacteria upon the Bodies of 

 Healthy Men and Animals. 



B. How Pathogenic Bacteria 



Reach the Body. 



1. Air-borne Infection. 



(a) Dust. 

 (6) Droplet. 



2. Soil-borne Infection. 



3. Water-borne Infection. 



4. Food-borne Infection. 



5. Animal Carriers. 



(a) Direct Contact. 

 (6) Indirect Transfer. 



(c) Mechanical 



Transfer. 



(d) Intermediary Host. 



6. Human Carriers. 



7. Contact Infection. 



8. Germinal and Prenatal 



Infection. 



C. Portal of Entry: Atria of In- 



vasion. 



1. Skin and Adnexa: Ear, 



Eye. SubcutaneousTis- 

 sue, Tonsils, Salivary 

 Glands, Nasal Cavity, 

 Lungs. 



2. Mucous Membranes: 



Mouth, Stomach, In- 

 testines. 



3. Geni to-urinary System: 



Vagina, Uterus, Ure- 

 thra, Urinary Bladder 

 and Ureter, Kidneys. 



D. Where Bacteria Multiply in 



the Body. 



E. Where and How Bacteria 



Escape from the Body. 

 VI. BALANCED PATHOGENISM; EPIDEMI- 

 OLOGY. 



I. DEFINITIONS AND LIMITS. 



THE most conspicuous and important function of bacteria in the 

 economy of Nature is to maintain a continuity between the Animal 

 and Vegetable Kingdoms by restoring in utilizable form to the Plant 

 World the elements contained in the complex organic compounds 

 which comprise the dead bodies of plants, animals and their products. 

 Bacteria dissipate much of the energy accumulated in these dead 

 bodies and oxidize the elements contained in them to inorganic, fully 

 mineralized salts. These salts are resynthesized by the chlorophyll- 

 bearing plants through the energy of sunlight to carbohydrates, 

 proteins and fats, and in these complex combinations the elements 

 are again available for animal food. 



The bacteria which live upon this dead organic matter, and whose 

 function it is to effect its degradation and ultimate mineralization, 

 are called saprophytic bacteria. They are specifically the most 



