The Use of the Microscope 



25 



Fig. 25. A medical microscope with a suitable illuminant. The microscope is an Ameri- 

 can Optical Company model No. 35. The lamp is an American Optical Company 

 model No. 735 and carries a neutral density filter. 



shown on the research scope discussed in the next section. The monocular 

 tube is perfectly adequate for class instruction, but for routine work or 

 prolonged observation the binocular tube saves so much eye strain that 

 it is well worth the extra money. Medical students buying their own mi- 

 croscope are strongly advised to obtain one with interchangeable monocu- 

 lar and binocular bodies, even though they can only afford, for the time 

 being, to purchase the monocular one. There is little difference in cost 

 and the subsequent purchase of the binocular body will adapt the in- 

 strument to the office routine of a practicing physician or his technician. 

 The tube is furnished with a three-lens turret— four-lens turrets are better 

 left to the research microscope, under which they will be discussed. 



Objectives. Microscopes of this type are best provided with XlO (16- 

 mm, N.A. 0.3) and X40 (4-mm, N.A. 0.65) dry objectives and with a 

 X90 (2-mm, N.A. 1.2) oil immersion. Achromatic objectives are perfectly 

 adequate for any type of use to which medical microscopes can legiti- 

 mately be put. Medical students sometimes buy apochromatic objectives 

 on the ground that since they are so expensive, they must be better; this 

 same reasoning would harness a race horse to a plow. Some manufac- 

 turers offer a X40 N.A. 0.75, or even 0.80, achromatic objective. This is 

 a desirable, but not necessary, investment and its short working distance 

 is a great disadvantage. A four-lens turret with the addition of a X-3.5 

 objective is a sheer waste of money because the condenser would have 

 to be removed every time it was used. The proper fourth lens on a micro- 

 scope of this kind is a X20 (8-mm, N.A. 0.75) achromat. These are ex- 

 pensive but extremely useful, particularly in histological work. 



