DIRECT EXAMINATION 



45 



means of the low power and make counts under the suitable high 

 powers. From ten to twenty of the ruled areas should be counted 

 md from these countings figure the average. It is desirable to 

 nake two or three mounts of each sample, thus giving the average 

 }f from twenty to thirty areas counted. The countings are to 

 3e made in areas free from pulp 

 'ragments and including all organ- 

 sms lying within the ruled bound- 

 ng lines and inclusive of half 

 iverages of those organisms which 

 ie across the rulings. All count- 

 ngs which present characters of 

 ioubt are omitted from the final 

 stimates. 



Those organisms which occur 

 within the cell-lumen of the vege- 

 table tissues are not to be counted. 

 To do so is practicably impossible 

 ind such countings, even if pos- 

 dble, would add nothing to the 

 value of the findings. In case the 



ells contain numerous bacteria this should be noted in the report, 

 as it certainly indicates decomposition of the material. The prin- 

 cipal decomposition changes due to the invasion of bacteria and 

 other organisms are, however, largely limited to the exterior of 

 cells, especially by those organisms which develop during or after 

 the factory processing. The numerical determinations are there- 

 fore limited to organisms which occur in the matrix and those which 

 have been washed from the exterior of cells by the thorough mixing. 

 The thorough mixing of the samples is a very important part of 

 the procedure. In the case of liquids and semili quids, mixing is 

 done by thorough shaking, and in the case of pastes and similar 

 materials, by means of a spatula or a small spoon. 



In making counts of very small or comparatively short bacilli, 



FIG. 9. Biirker ruling, useful in 

 making counts of milk fat globules, 

 spores, and yeast cells. The average 

 of many counts is taken. (Carl Zeiss.) 



