APPLICATION OF THE METHODS OF 

 BACTERIOLOGY. 



CHAPTER XIV. 



To obtain material with 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, place it in a warm spot 

 (temperature not to exceed that of the human body 

 — 37.5° C), and allow it to remain undisturbed. In 

 from twenty-four to thirty-six hours there will 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 are due in some cases to the presence or 

 absence of color; in others to 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 of 

 irregular, ragged deposit. All these gross appear- 

 ances are of value in aiding us to distinguish between 

 these colonies — for colonies they are, and under the 

 same conditions the organisms composing each of them 

 will always produce growth of exactly the same ap- 

 pearance. It was just such an experiment as this, 



§81 



