118 Microbes and You 



viously in Chapter 4. To be assured of a good harvest a farmer 

 not only has to plant good seed in fertile ground, he must also 

 rely upon Providence to furnish the necessary warmth, sunshine, 

 and moisture to allow these seeds to germinate and to develop into 

 mature plants. Once the plants begin to grow, the care-taker 

 must control inevitable pests— the insects and the diseases to which 

 these growing plants are susceptible. 



A bacteriologist in cultivating microbes is able to control these 

 factors of heat, moisture, and contaminants. If he knows the food 

 requirements of his proposed crop, and if he understands the ele- 

 mentary principles of aseptic technic (not allowing undesirable 

 organisms to get into his cultures), the unwanted "weeds" can be 

 eliminated, and he can be assured of harvesting a good crop of 

 pure culture. Controlled cultivation is within the reach of all 

 laboratory workers who follow the fundamental rules of the game. 



No reliable physiological determinations can be made on mixed 

 cultvires of bacteria. The purity of the microbial culture is just as 

 important, if not more so, than it is in growing grain crops. In the 

 latter case, should an undesirable seed find its wav into the batch, 

 the growing plant can readily be pulled up and discarded prior to 

 the harvest. But in the bacteriology laboratory, once the contami- 

 nant gains entrance into a culture, especiallv liquids, it may be 

 necessary to plant a new crop, sometimes repeatedly, until the cul- 

 ture has been purified. 



Bacteria are ubiquitous, and if technicians will keep that 

 thought constantly in mind, proper technics for handling and cul- 

 tivating pure bacterial masses are more likely to be employed. 

 Careful attention to what may seem like exacting details will pay 

 dividends in the long run. Not onlv will contamination be mini- 

 mized, but the worker may save himself the painful experience of 

 contracting a laboratoiy infection when he handles pathogenic 

 organisms. 



PURE CULTURE ISOLATION TECHNICS 



There are very few places where pure cultures of organisms 

 exist in nature. As long as bacteria are found practically every- 



