which number corresponds to the index and, turning 

 the collar back to its closed point, go through the same 

 procedure as carefully as at first. When the best point 

 is again reached look for the number and see whether 

 it agrees with the first ; very likely it does not, which 

 is owing to a lack in the faculty of perception, due to 

 a too slight acquaintance with the phenomena. These 

 trials should be repeated until the proper sensitiveness 

 of feeling in making the adjustments is acquired and 

 until they can be made to correspond with certainty 

 to at least within two divisions. When it is found 

 after repeated trials that sufficient skill has been 

 acquired, mark the number upon the slide. For future 

 examination of the same slide, this will facilitate work 

 and give the assurance that the best results are thus 

 obtained without further trial by simply referring to the 

 recorded number. 



On stained Bacteria and Micrococci focus briskly 

 with the fine adjustment to either side of exact focus. 

 There will be an expansion of the outline of the object 

 both when within and without the focus. 



If the greater expansion or coma is within the focus, 

 or when it is necessary to raise the objective, there is 

 spherical over-correction and the adjustment must be 

 closed. 



If the greater expansion is below the focal plane, 

 there is sphericdl under-correction and the adjustment 

 should be opened. 



145 



