BACTERIA, MOLDS, AND MILDEW 239 



propagated. This takes place by means of spores in the case 

 of molds, mildews, and some bacteria, and by means of 

 division with most bacteria. 



Bacteria are often mentioned only as disease bacteria. 

 We must not get the idea that all bacteria are bad, for such 

 is not the case. There are only about twenty-two species 

 that are harmful to man, while there are several thousands of 

 the kind which aid man in many ways. In a similar manner 

 the white corpuscles of the body are helpers, whose function 

 it is to protect us from the inroads of the harmful bacteria. 



Other bacteria are used in the animal system to assist di- 

 gestion, and it is probable that digestion would be of longer 

 duration, if it were not for these agents. Bacteria enable 

 plants to absorb nitrogen from the air; they cause the decay 

 of animal matter, as well as vegetable matter, so as to render 

 proper food supplies available for plants. In fact, their ad- 

 vantages are so great that they cannot be enumerated in 

 this place. Under agriculture, mention has been made of 

 the importance of the nitrogen-fixing bacteria, as well as the 

 bacteria of decay. 



References : 



1. 1407:228-238. Bacteria. 



2. 1501 : 382-390. Bacteria and Disease. 



3. 1503:168-172. Bacteria. 



4. 1601 : 124-130. Nitrogen-fixing Bacteria. 



5. 1605 : 97-99. Life in the Soil. 



6. 1901 : 1-12. Introduction to the Study of the Lower 



Plants. 



7. 1901 : 12-39. General Nature of Molds. 



8. 1901 : 100-114. General Nature of Bacteria. 



9. 1901 : 124-131. Dead Food Bacteria. 



10. 1901 : 203-211. Disease Bacteria. 



11. 1901 : 212-240. Prevention of Contagious Diseases. 



