46 



BACTERIOLOGICAL METHODS 



some difficulty is caused by those organisms which happen to be 

 vertically suspended in the counting chamber, thus presenting an 

 end view which gives the appearance of small granules or spherical 

 particles which the comparatively inexperienced observer may not 

 recognize, or which may be mistaken for inorganic particles or 

 organic particles other than microbic. In case of doubt, allow the 



Fig. 10. — Tomato pulp cells in normal catsup. The cells are large, thin-walled, 

 containing granular particles. The coloring matter of the tomato frequently ap- 

 pears as deep scarlet-red crystalline particles usually arranged in groups within the 

 cell. — {Howard, Yearbook U. S. Dept. of Agriculture, 1911.) 



mount to remain at rest for 10 or 15 min., thus allowing the 

 bacilli to settle to the bottom of the cell where they will assume 

 the horizontal position, thus presenting the long axis to view 

 and making counting easier. 



In order that all of the cells (individuals) of the bacilli may be 

 counted, it is necessary to use a high power (480 to 500 diam.). 

 Lower powers are not satisfactory for counting bacteria. For 



