138 THE MICROSCOPE. Sept. 



A movable stage, while not an absolute necessity, 

 neither simply a luxury, is yet a great convenience and 

 a xjleasure to work with. For biological work a con- 

 denser becomes almost a necessity, and as it must be ad- 

 justed for different objectives, the sub-stage must be 

 moveable on the sub-stage bar; a condenser can then be 

 supplied at any future time, without additional expense 

 for after changes in the stand. 



The mirror should be double, plain and concave, and 

 swing on the mirror bar and be capable of being brought 

 nearer to or further from the stage. 



Two eyepieces should accompany the stand, A and B, 

 or perhaps, C, will usually meet the requirements. 



For bacteriological examination a good dry h, or better 

 still a 1-10 or 1-12 inch homogeneous immersion objective 

 will be necessary; but for all ordinary professional use 

 two objectives will answer every purpose for a longtime 

 including urinary examinations for the various crystalline 

 deposits, tube casts, blood, pus, etc. A 1 inch of an an- 

 gular aperture of 25 degrees, and a 1-5 inch of angular 

 aperture of V5 or 80 degrees: or a 2-3 or 3-4 inch object- 

 ive of 27 degrees of angular aperture, and a 1-6 inch ob- 

 jective of 110 degrees of angular aperture will be amply 

 sufficient. Either the 1-5 or 1-6 objective with the C 

 eyepiece will, with a little eye training, on well stained 

 specimens show the bacilli of tuberculosis. The question 

 is not so much how many diameters will the objective 

 magnify but, what will it show. A well corrected low 

 power objective of wide angle will show more of detail 

 and structure than a poorly corrected and narrow angle 

 high power objective. 



It is true that from an optical standpoint objectives 

 give more detail as they increase in their angular aper- 

 ture yet the highest class of objectives are not always to 

 be preferred. The lenses here advised are not expensive 

 glasses, and yet they will do fine enough work of the 



