MICROSOMES 



205 



MICROSOMES 



up the microscope apply to the oil 

 immersion lens. When dry lenses are 

 to be used omit step 2. 



1. Clean the slide with alcohol. 

 Put a drop of xj-lol on the oil immersion 

 lens and polish it with lens paper. 

 Do the same for the eye piece. 



2. Raise the condenser so that its 

 upper surface is on a level with the 

 stage, or slightly below it. Put a drop 

 of immersion oil on the condenser and 

 lay the slide down. Put a drop of oil 

 on the slide, lower the lens, and focus 

 as usual. 



3. Open the diaphragm wide, and 

 removing the eye piece, look down the 

 tube. Adjust the position of the light 

 source and mirror so that the aperture 

 appears sj^mmetrically illuminated. 



4. At this point the aperture should 

 look like a bright disk surrounded by a 

 rim of dim illumination. Now, close 

 down the diaphragm until about nine- 

 tenths of the area of bright central 

 field remains visible. Replace the 

 eye piece. The N. A. of condenser 

 and objective are now approximately 

 equal. 



5. Modify the brightness of the image 

 for visual comfort by altering the in- 

 tensity of illumination; not by altering 

 the diaphragm. If the image is too 

 bright put tissue paper over the lamp 

 or pull the lamp away and readjust by 

 repetition of Steps 3 and 4. If the 

 image is not bright enough move the 

 lamp in, and if necessary dispense with 

 the substage mirror. As the final step, 

 try a slight change in the position of 

 the condenser, but avoid breaking the 

 oil pool between the condenser and the 

 slide. 



Resolving power may be improved 

 somewhat for striated, or periodic, 

 structures by using oblique illumina- 

 tion. Light is sent diagonally from 

 below so that only part of it enters 

 the objective, with the striations (as in 

 muscle) lying across the direction of 

 the light. If the condenser is not 

 laterally movable it should be masked 

 below so that light enters only from one 

 side. By trial and error a favorable 

 orientation of condenser, slide and 

 mask can be found. 



The limitations imposed on the re- 

 solving power of the conventional 

 microscope cause no inconviences in 

 general histology. It is with the finer 

 details of cytology that need is felt 

 for greater resolution. As is obvious 

 from the formula R = X/2 N. A., either 

 an increase of N. A. or a decrease of X 

 will reduce the value of R. The best 

 available oil immersion objectives and 

 condensers are rated at 1.40 N. A. 



A special lens working at 1.60 has been 

 designed, but the improvement in re- 

 solving power over one at 1.40 is not 

 important. Fortunately we can ob- 

 tain the shorter values of X by em- 

 ploying ultra-violet light and photog- 

 raphy (see ultraviolet-microscope). 



A word should be said in favor of 

 water-immersion objectives, items for- 

 merly found in every laboratory of 

 microscopy but now no longer listed in 

 the catalogues of American manufac- 

 turers. These are made in a series of 

 magnifications, and in resolving power 

 are intermediate between air and oil- 

 immersion objectives. For study of 

 living aquatic organisms and tissue cul- 

 tures the lOX and 44X objectives are 

 very useful since they are made to be 

 lowered directly into the medium. 

 For histological slide material the high- 

 power water-immersion objective is 

 probably not inferior to the oil-immer- 

 sion, besides being more convenient 

 to use. 



It is commonly believed that a bin- 

 ocular, i. e., two eyepiece, microscope 

 is superior to the monocular because it 

 affords stereoscopic vision. Actually, 

 it cannot be so since a single objective 

 forms only one primary image regard- 

 less of whether it be viewed by one or 

 two eyes. Nevertheless our habit of 

 seeing with two eyes probably creates 

 an illusion of stereoscopic vision with 

 the binocular microscope. On the 

 other hand a binocular microscope em- 

 ploying two objectives on a pair of 

 converging tubes does provide stereo- 

 scopic views. The dissecting micro- 

 scope is built on this pattern, having 

 in addition a set of reversing and erect- 

 ing prisms so that the final image is 

 normally orientated. Magnifications 

 above 30X become rather useless for 

 dissection purposes because the depth 

 of focus is greatly reduced. Manipula- 

 tion is usually by hand. 



See Centrifuge, Color Translation, 

 Darkfield, Electron, Phase Contrast, 

 Metallurgical, Polarizing, Reflecting 

 and Ultraviolet Microscopes. Many 

 excellent books on microscopes and 

 photomicrography are available. The 

 following are suggested: Gage, S. H., 

 The Microscope. Ithaca: Cornstock, 

 1941, 616 pp. Shillaber, C. P., Pho- 

 tomicrography in Theory and Prac- 

 tice. New York: John Wiley and Sons, 

 1944, 773 pp. Wredden, J. H., The 

 Microscope, Its Theory and Applica- 

 tion. New York: Grune and Stratton, 

 1948, 296 pp. 

 Microsomes (G. mikros, small, soma, body). 

 Term introduced by Hanstein in 1880 

 originally to indicate tiny granules — as 



