PART II. 



CHAPTEE I. 



NON-PATHOGENIC BACTERIA. 



THE study of the non-pathogenic bacteria is of interest 

 largely from a commercial point of view, as many of these 

 organisms play a very important part in the manufacture 

 of certain articles of food. 



In the bacteriologic laboratory it is convenient to begin 

 the study of bacteria, and the methods of their culture and 

 development, with the non-pathogenic group, because most 

 students are inclined to underestimate the danger involved in 

 handling bacteria and the possibility of infection. The study 

 of the pathogenic bacteria is not taken up until the technique 

 has been mastered. 



The non-pathogenic bacteria are so numerous that it is 

 impossible in a work of this size to consider them all or at 

 any length. We shall limit the enumeration to such of these 

 organisms which are either very 'common; or which, because 

 of their resemblance to important pathogenic bacteria, are 

 noteworthy. Furthermore, the student can easily obtain pure 

 cultures of these germs for laboratory study. Most of the 

 non-pathogenic bacteria are found either in water or in the air. 



Bacillus subtilis : One of the most common varieties is the 

 Bacillus subtilis or hay bacillus. It is found in hay infusions, 

 water, soil, air, feces, and decomposing liquids. Cultures are 

 obtained very easily, and particularly when not wanted. 

 Most of the culture contaminations which occur in the labora- 

 tory are with the hay bacillus. 



The hay bacillus is a thick rod, about three times as long 

 as broad, with rounded ends, and resembles the anthrax 



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