CHAPTER XXXVI 

 BACTERIA AND DISEASE 



For ages mankind has been nearly helpless before the 

 ravages of contagious diseases. Ignorant of their real 

 cause, people have attributed such diseases to "effluvia," 

 to poisons carried in the air, and in former ages to posses- 

 sion by evil spirits. We know now that they are produced 

 by some kind of an organism that can be transferred from 

 one individual to another. Many diseases are caused by 

 protozoans, as is the case with malaria, Texas fever and 

 amoebic dysentery. Some diseases (ringworm) are pro- 

 duced by fungi. A few diseases, such as filariasis, trichi- 

 nosis and the itch, are caused by higher animals. But 

 the greater part of our contagious maladies are due to very 

 minute organisms known as bacteria. 



These bacteria are the simplest known forms of life. 

 They are as a rule exceedingly minute. A great many 

 species appear like short rods (Bacilli), some are nearly 

 spherical (Cocci), while others are spiral (Spirillum, 

 Spirochetes). Some of the species are furnished with one 

 or more flagella by means of which they may move .about. 

 Bacteria usually multiply by fission, and so rapid is their 

 multiplication that a single bacillus may give rise to 

 16,700,000 individuals in twenty-four hours. At times, 

 and especially under unfavorable conditions, bacteria 

 may produce small, rounded bodies called spores which 

 are unusually resistant to heat, cold or dryness. When 

 better conditions occur these spores give rise to other 

 bacteria. 



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