Economic Importance of Plants 255 



About 150 species of bacteria (phylum Schizomycophyta) are directly 

 or indirectly responsible for human diseases. The following are a few 

 common, representative human diseases of bacterial origin (Fig. 34) : 



Boils, carbuncles, abscesses, etc. 



Internal and general infections 



Many cases of "sore throat" 



Erysipelas 



Scarlet fever 



Meningitis 



Gonorrhea 



Pneumonia 



Anthrax or splenic fever 



Diphtheria 



Typhoid fever 



Paratyphoid fevers 



Tuberculosis 



Leprosy 



Malta or undulant fever 



Plague or "black death" 



Tularemia or "rabbit disease" 



Whooping cough 



Tetanus or "lockjaw" 



Gaseous gangrene 



Botulism (toxic food poisoning) 



Staphylococcus aureus 

 Streptococcus pyogenes 

 Streptococcus hemolyticus 

 Streptococcus erysipelatis 

 Streptococcus scarlatinae 

 Diplococcus intracellularis 

 Neisseria gonorrhea 

 Diplococcus pneumoniae 

 Bacillus anthracis 

 Corynebacterium diphtheriae 

 Eberthella typhosa 

 Salmonella paratyphi (Type A) 

 Salmonella schottmiilleri (Type B) 

 Salmonella hirschfeldii (Type C) 

 Mycobacterium tuberculosis 

 Mycobacterium leprae 

 Brucella melitensis 

 Pasteurella pestis 

 Pasteurella tularense 

 Hemophilus pertussis 

 Clostridium tetani 

 Clostridium welchii and others 

 Clostridium botulinum 



From the consideration given above, one might imagine that all bac- 

 teria are harmful. This is not the case. Most bacterial organisms are 

 neither harmful nor beneficial; less than three hundred have been spe- 

 cifically proved pathogenic, and an ever-increasing number is found to 

 be very beneficial in many ways. Bacteria are valuable in decomposing 

 plant and animal remains so that the original constituents may again 

 be used by future living organisms. Bacteria arc also employed in the 

 process of tobacco curing as well as in the retting process followed in 

 the preparation of flax for industrial purposes. Certain species of bac- 

 teria play an important role in the fermentation of sauerkraut, giving it 

 the characteristic odor and flavor. Other species of bacteria are bene- 

 ficially associated in the manufacture of butter, cottage cheese, and 

 other cheeses. Specific bacteria are responsible for the use of free nitro- 

 gen of the air by the plants of the legume family. This is more fully 

 discussed in the nitrogen cycle. Other organisms are also associated 

 with other nitrogen transformations in the soil. The manufacture of 

 vinegar is also dependent upon the fermentation of certain juices by 

 acetic acid bacteria. It is thought that bacteria, and possibly other 

 microorganisms, are responsible for the decomposition of the remains of 

 organisms with the formation of crude oil and natural gas. It is also 



