MICROMETRY 



203 



MICROSCOPES 



Considerable deviations are possible 

 in the matter of the microinjection 

 technique. For example, if it is deemed 

 desirable to have no air in the system, 

 the shafts of the capillary tubing, on 

 which the microtips are drawn, may 

 previously be filled with either oil or 

 water. By using some ingenuity the 

 entire microinjection apparatus can be 

 built in the laboratory, the parts re- 

 quired being a Luer syringe, hypodermic 

 needles the shafts of which can be cut 

 off, a strip of flexible brass or copper 

 tubing, glass tubing and of course the 

 operator's constant companion: a stick 

 of deKhotinsky cement or an analo- 

 gous superior sealing wax. 



The instruments are generally supplied 

 in pairs, one part carrying a micro- 

 needle for holding the tissue to be 

 injected, the other carrying the micro- 

 pipette. For microdissection, the in- 

 strument carries two needles, each of 

 which can be operated independently. 

 Wilhelm Pfeffer, to whom we owe the 

 term "plasma membrane" for the limit- 

 ing boundary of protoplasm, stated, in 

 one of his papers in 1887, that an instru- 

 ment with which one could operate 

 delicate needles and pipettes in the 

 field of a compound microscope would 

 go far toward the elucidation of the 

 nature of living cells. Pfeffer's dream 

 has been realized in the development of 

 the special field of science called today 

 Micromanipulation or Micrurgy. 



Of general interest, and also for many 

 details not described elsewhere, are the 

 following: Barber, M. A., Philippine J. 

 Science, B, 1914, 9, 307; Chambers, R., 

 Anat. Rec, 1922, 24, 1; P^terfi, T., in 

 methodik der wissensch. Biologic, 1928, 

 1 (4), 5; and Schouten, S. L., Zeit. f. 

 wiss. Mikr., 1934, 51, 421. An excellent 

 book which covers a broad range of the 

 field of Micrurgy is that edited by 

 J. A. Reyniers on Micrurgical and 

 Germ-Free Techniques, C. C. Thomas, 

 1943, an article on micromanipulation 

 by Chambers, R. and C. G. Grand, 

 Encyclopaedia Britannica, 1948. 



Micrometry is the measurement of an object 

 observed microscopically. This can be 

 done either by using an ocular microm- 

 eter in which there are lines which can 

 be accurately moved the length of the 

 structure to be measured or by inserting 

 a ruled disc in an ordinary ocular with 

 which it can be compared. Both must 

 be standardized in relation to a microm- 

 eter slide generally ruled with lines 10m 

 apart. See Cell Measurements. 



Micromicron (nn) = 1/1 ,000,000th part of a 

 micron = 1/1, 000 ,000 ,000th part of a 

 mm. = 10- » mm. = 0.000,001 micron = 

 10~^A. Unfortunately often used syn- 



onymously with o millimicron (m/i) = 

 0.001 micron = lOA. 



Micron (Gr. Mikros, small) expressed by 

 Gr. letter n = approximately 1/25,000 

 inch = 1/1000 part of a mm. = 0.001 

 mm. = 10-3 mm. = 10,000 A (see 

 Millimicron and Micromicron). 



Microphotometer, see Photoelectric. 



Microradiographic examination. This con- 

 sists of magnification of a Roentgen ray 

 image after it has been registered pho- 

 tographically. The essential point is 

 to use film of very fine grain emulsions. 

 Thus the Gevaert Lipmann emulsion 

 permits enlargement 300 times without 

 much loss of detail. In some cases it 

 is helpful before microradiographic 

 examination to increase the absorption 

 of Roentgen rays by "absorption stain- 

 ing" through adding radio-opaque mate- 

 rials such as barium sulp'aate and thoro- 

 trast. The application of this technique 

 in the study of biologic materials 

 is described and illustrated by Clark, 

 G. L. and Bick, E. J., in Glasser's Medi- 

 cal Physics, 730-733. 



The importance of extremely soft 

 Roentgen rays and the properties of 

 fine-grained emulsions are described 

 by Engstrom, A. and Lindstrom, B., 

 Acta Radiol., 1951, 35, 33-44. See also 

 their illustrations of striated muscle 

 fibers and of bone by microradiography. 



Microrespirometer to indicate production of 

 carbon dioxide by bacteriophages, 

 viruses and bacteria (Bronfenbrenner, 

 J., Proc. Soc. Exp. Biol. & Med., 1924, 

 22, 81-82. See Capillary Respirometry. 



Microscopes (From Cowdry's Histology, 

 1950). While excellence in histological 

 technique is important, knowledge of 

 microscopes and of how to get the best 

 service out of them is also important. 

 There are several kinds from which a 

 choice must be made of the one capable 

 of yielding the information required. 

 The following account of what these 

 instruments are, what their particular 

 use is, what their limitations are, sup- 

 plemented by leading references to 

 literature on the subject is offered for 

 guidance. It was written for Cowdry's 

 Histology by Dr. T. B. Rosenthal. 



The ordinary compound microscope is 

 a precision optical instrument designed 

 to give magnified images of 50 to 1200X. 

 Daylight, or strong artificial light, is 

 used to illuminate by transmission a 

 more or less thin, flat, transparent 

 object. The image appears in its nat- 

 ural form and color, but inverted and 

 reversed in position, at a distance of 

 about 10 inches from the eye. Height 

 and depth are not reversed, however, 

 so it is possible to judge or measure 



