CHAPTER XXVI 

 USING THE MICROSCOPE 



The investigator who desires to see all that his microscope is 

 capable of showing must study the optics of his instrument. The 

 fundamental principles are presented in any good textbook of physics. 

 Excellent practical hints are given in two booklets published by the 

 leading American optical companies. These booklets tell the begin- 

 ner how to set up the microscope, how to keep it in order, and give 

 directions concerning illumination, dry and immersion objectives, 

 mirror, condenser, diaphragm, and various other things (Fig. 102). 

 They were doubtless written for advertising purposes, but since they 

 advertise by giving directions for securing the best results with the 

 microscope, the information is very reliable. The Spencer Lens 

 Co., of Buffalo, New York, and The Bausch & Lomb Optical Co., 

 of Rochester, New York, furnish these booklets free of charge. 



In the histological laboratory where preparations are being made 

 the microscope is in constant danger. A cheap microscope with a 

 16 mm. objective and one ocular, such an instrument as can be got 

 for $20 or less, can be used for examining preparations while they are 

 wet with alcohols, oils, or other reagents. If it is necessary to use 

 a better instrument for such work, cover the stage with a piece of 

 glass an old lantern slide is of about the right size and be extremely 

 careful not to get reagents upon the brass portions. 



MICROMETRY 



Everyone who expects to become at all proficient in the use of 

 the microscope should learn to measure microscopic objects and 

 should learn to form some estimate even without measuring, just 

 as one guesses at the size of larger objects. In any measurement 

 one should note the tube length, which is usually 160 mm. Since 

 the use of the nosepiece is universal, it is convenient to have the 

 length measure 160 mm. when the tube is pushed in. Some com- 

 panies still make the tube so short that it must be pulled out about 



280 



