ELASTIN 



112 



ELECTRON MICROSCOPY 



of blood vessels, a useful combination 

 of Weigert's elastic tissue stain and 

 Masson's trichrome stain has been 

 worked out by Mendeloff, J., Am. J. 

 Clin. Path., 1943, Tech. Suppl. 7, 65. 

 Deparaffinize sections in usual way, 

 wash thoroughly in water and stain in 

 Weigert's Resorcin Fuchsin mixture for 

 60 min. Wash quickly in Acid Alcohol, 

 dehydrate and differentiate in abs. ale. 

 till section is only faintly red. Pass 



through 70% ale. to aq. dest. and stain 

 in Harris' Alum Hematoxylin 8 min. 

 Differentiate in water 5 min. Stain in 

 Ponceau acid fuchsin mixture (see Mas- 

 son's Trichrome) 5 min. Wash thor- 

 oughly and place in 3% aq. phospho- 

 tungstic acid, 10 min. Wash again 

 thoroughly in water and stain with 

 light green. Transfer directly to 1% 

 acetic acid, 3 min. Do not wash but 

 dehydrate, clear and mount in Gum 

 Damar. Elastic tissue, blue -black; 

 smooth muscle, red; collagen, green. 



Elastin, see Elastic Fibers. 



Electric Tissues of fishes, methods for are 

 given by Dahlgren (McClung, 1950, 

 p. 343). 



Electrical Resistance and capacity or 

 Impedence. By employing alter- 

 nating currents of varying frequencies 

 figures for apparent resistance and 

 capacity can be obtained. Red cells, 

 yeast cells, ova etc. have been investi- 

 gated. The technique is not micro- 

 scopic but the data have an important 

 bearing on structure. In view of the 

 wide variety of cells studied it is inter- 

 esting, as Danielli remarks (Bourne, 

 p. 42), that a definite pattern should 

 emerge of a cell plasma membrane only 

 10~*-10~' cm. in thickness corresponding 

 to a specific resistance of lO^^-lO" ohms. 



Electrodes. See the several varieties de- 

 scribed in full with literature references 

 and diagrams by Click, pp. 183-188. 



Electromagnet Technique to determine elas- 

 ticity (Heilbroun, A., Jahrb. wiss. Bot., 

 1922, 61, 284), employed by Seifriz, W. 

 and Hock, C. W. (Paper Trade J., 

 1936, 102, 36) and described by Cham- 

 bers, R. W. and Kopac, M. J. in Mc- 

 Clung's Microscopical Technique, 1950, 

 p. 542. 



Electron Microscopy — Details originally 



Erovided by Dr. W. L. Simpson; revised 

 y Dr. T. B. Rosenthal, Dept. of Anat- 

 omy, Washington University, St. Louis. 

 June 6, 1951. 



1. Transmitted electron beam type. 

 The relationship of the wave length 

 (X) of light employed and to the nu- 

 merical aperture (N.A.) of a lens system 

 as expressed in the relation R.P. equals 



T;^—r- proved for many years an ap- 



parently insurmountable limitation to 

 the biologist's desire to investigate di- 

 rectly minute structure of cells and 

 tissues. Even when ultraviolet light 

 of 2250A was employed the limit of 

 resolution was 0.08 y. in & system of 

 N.A. 1.40. With visible light the limit 

 was approximately 0.2 y.. On the as- 

 sumption that the angle of visual acuity 

 is 1 minute of arc, the greatest mag- 

 nification that was practical with visi- 

 ble light ranged from 1750 to 2100 times. 

 There is, of course, no limitation to the 

 actual magnification that may be 

 achieved. Increases beyond the limit 

 mentioned, however, do not reveal new 

 structures. As long as this was true 

 there seemed no hope of direct confir- 

 mation of the amazing findings made 

 possible by such new methods as x-ray 

 diffraction, ultracentrifugation studies, 

 chemical studies of virus structure, and 

 polarized light methods. 



Small wonder is it then that the 

 biologist has grasped with enthusiasm 

 at the possibilities of visualizing ultra- 

 microscopic structure by means of 

 devices that have grown from the fertile 



