PRACTICAL APPLICATION OF THE METHODS 

 OF BACTERIOLOGY. 



CHAPTER XVI. 



To obtain material upon which to begin work. 



EXPOSE to the air of an inhabited room a slice of 

 freshly steamed potato or a bit of slightly moistened 

 bread upon a plate for about one hour. Then cover it 

 with an ordinary water-glass and place it in a warm spot 

 (temperature not to exceed that of the human body 

 37.5 C.), and allow it to remain unmolested. At the 

 end of twenty-four to thirty-six hours there can be 

 seen upon the cut surface of the bread or potato small, 

 round, oval, or irregularly round patches which present 

 various appearances. 



These differences in macroscopic appearance con- 

 sist in some cases in the presence or absence of color ; 

 again in a higher or lower degree of moisture; in some 

 instances a patch will be glistening and smooth while its 

 neighbor may be dull and rough or wrinkled. Here 

 will appear an island regularly round in outline and 

 there an area covered by an irregular ragged deposit. 

 All of these gross appearances are of value in aiding us 

 to distinguish between these colonies for colonies they 

 are and under the same conditions the organisms com- 



