BACTERIA IN THE INDUSTRIES 159 



moisture and sunlight. Most bacteria require an ample supply of air 

 (free oxygen) and these are spoken of as aerobes. A comparatively smaller 

 number thrive in the absence of air (free oxygen) and these are called 

 anaerobes. The soil bacteria are essentially aerobes, as is perhaps 

 self-evident. 



Bacteria are however not the only microorganisms found in the soil. 

 Soil also contains minute algae, fungi and microscopic single-celled ani- 

 mals (protozoa), to say nothing of earthworms, insects and other higher 

 animals, concerned in certain soil changes of minor importance. The pro- 

 tozoa, algae and fungi (molds) may be and are, of great significance in 

 crop growing. In a general way it may be stated that most of the algae, 

 the fungi and the protozoa work antagonistically to the bacteria which 

 are normal to soils. It must however not be supposed that all of the 

 bacteria found in the soil are useful or beneficient. Occasionally harmful 

 bacteria develop in certain soils, causing plant diseases and otherwise 

 interfering with plant growth. It is the aim of modern scientific agri- 

 culture to so regulate cultural operations as to encourage the optimum 

 development of the beneficient soil bacteria, reducing at the same time, to a 

 minimum, the development of all harmful soil organisms (bacteria, proto- 

 zoa, molds, etc.). 



Incidentally it may be mentioned that soil harbors bacteria and other 

 organisms which play no part in plant growth or in agriculture proper; 

 such as the lock jaw bacillus (Bacillus tetani), the anthrax bacillus (B. 

 anthracis), the bacillus of malignant oedema (B. Welchii), the tuberculosis 

 bacillus (B. tuberculosis), the typhoid bacillus (B. typhosis), and others. 

 Soils may also harbor the cause of rabies, of foot and mouth disease, the 

 larvae of hook worm and the larvae of other intestinal parasites, besides a 

 host of minute organisms injurious to plants and to the lower animals. 

 Swamp lands are the breeding places of the malaria and yellow fever carry- 

 ing mosquitoes. Proper drainage and tillage of soils tends to check and 

 to reduce to a minimum the development of these highly objectionable 

 soil inhabitants and thus the farmer becomes a most useful worker in 

 behalf of public health and sanitation. Proper sewage disposal prevents 

 dysenteries and typhoid, cholera and many other dread diseases. Every 

 farmer should have a good general knowledge of rural sanitation. 



Historical. Crops have been grown for thousands of years. The 

 earliest cultural methods were crude indeed and at that remote period 

 nothing was known about soil bacteriology, but even in Virgil's time 

 (about 70 B.C., hence nearly 2,000 years ago) agriculture had made some 

 notable progress, for the noted poet in his Georgics, clearly sets forth the 

 value and importance of turning over the soil, the beneficial results of 

 crop rotation and the value of vetch and of other leguminous crop plants 



