xix BACTERIA AND DISEASES 297 



watery fluid which becomes sticky later, so that the 

 eyelids may be firmly gummed together every morning. 

 The eyes become weak and highly sensitive to ordinary 

 light. The person afflicted should be isolated until he 

 recovers. 



SUMMARY OF THE MAIN POINTS 



1. Bacteria are very small microscopic organisms belonging 

 to the vegetable kingdom. There are three classes as to shape, 



the coccus, the bacillus, and the spirillum. 



2. Bacteria multiply very rapidly, and some kinds can resist 

 cold, moisture, and heat so successfully that they can live under 

 conditions which prove fatal to all other forms of life. 



3. Most of these organisms are useful to man. They cause 

 decay or decomposition in animal and vegetable matter, manu- 

 facture a large amount of carbon dioxid for the use of plants, 

 act as scavengers to clean up dead matter about us, form certain 

 commercial products, and make it possible for some plants to 

 obtain nitrogen directly from the air. 



4. Some bacteria can grow and develop best in the human 

 body if favorable conditions are present. 



5. Most of the diseases are due to the poisons which the 

 bacteria produce in the body, and not simply to the presence 

 of the organisms. 



6. The bacteria get into the body through the air passages, 

 through the alimentary canals with foods and water, and through 

 bites and wounds in the skin. 



7. The body, if in good health, has the power to resist the 

 bacteria. The white corpuscles destroy vast numbers, the 

 plasma of the blood and lymph kills many, and the serum of 

 the blood may contain antitoxins which destroy the effects of 

 the poisons produced by the germs. 



8. If the tissues and organs have a high degree of vitality, 



