DYES 



105 



EAR 



processes inserted into tunnels encircled 

 by capillary loops; but a lesser number, 

 resting on connective tissue, occupy 

 sockets. After brief treatment of fresh 

 lungs with ammoniacal silver solution, 

 many of the dust cells are blackened 

 and their mode of insertion into mural 

 vaginae are made clear (Macklin, C. C, 

 Anat. Rec, 194S, 100, 693). After with- 

 drawal of such processes these vaginae 

 or tunnels, now vacated, have become 

 pores (Macklin, C. C, J. of Thor. 

 Surg., 1938, 7, 536-551). These mural 

 phagocytes may have as many as four 

 functional air faces or particle receptors 

 of varying area. These often conform 

 to the contour of the alveolar wall, 

 but, in presumably active cells, project 

 into the air space. The edges may 

 extend upon adjacent capillaries and 

 have been mistaken for respiratory 

 squames by some workers. They are 

 sister cells of the alveolar granular 

 cells (septal cells, niche cells, etc.) and 

 the term "pneumonocyte" (which see) 

 includes both types. Dust cells may be 

 recovered from fresh lungs by the 

 "gash-irrigation" and "wash-out" 

 methods (which see), and studied in 

 fresh mounts or after being dried and 

 stained like a blood smear. Mito- 

 chondria are scarce or absent in them. 

 One hour after e.xposure to carmine 

 particles in the inspired air they con- 

 tain much carmine, which is almost 

 completely absent on the remaining 

 alveolar wall surface, and almost 100% 

 are inserted into the walls. One week 

 after such dusting, however, only 35% 

 are mural phagocytes, the rest being 

 free. Since dust cells are constantly 

 being lost to the body they must be 

 replaced correspondingly by the mul- 

 tiplication of sister cells remaining in 

 the walls. Dust cells often show bi- 

 zarre shapes and a common one is that 

 of a dumb-bell in which the middle 

 narrow bridge occupies a pore. Such 

 cells are probably not in transit from 

 one avleolus to another. 



Histocj^tes of the lung connective 

 tissue often pick up dust particles which 

 have passed the inefficient surface guards 

 of the broncho-alveolar system. These 

 are regarded as quite different from the 

 endodermal alveolar phagocytes. 

 Great amounts of such aberrant dust 

 may accumulate and may give rise to 

 disease processes. 



Dyes, see "standardization of Stains" pp. 

 xxvii-xxx of this book and Staining. 



Dysentery, see Endamoeba. 



Dysprosium, see Atomic Weights. 



Ear— Written by W. P. Covell, Dept. of 

 Anatomy, Washington University, St. 

 Louis 10, Mo. October 26, 1951— Micro- 



scopic examinations of the ear are 

 nearly always made on sections. This 

 is understandable, but it is possible that 

 the study of still living tissues, removed 

 by careful and minute dissections, is a 

 field of considerable promise. The close 

 apposition of epithelial and nervous 

 components to bone necessitates de- 

 calcification except in the case of young 

 embryos. The frequent use of celloidin 

 in place of paraffin for imbedding is 

 occasioned bj^ the wide range of diver- 

 sity in resistance of the organ to the 

 microtome knife, fluid containing 

 lumina being surrounded bj' hard dense 

 bone. The histological techniques 

 actually in use for the ear are fewer in 

 number and more limited in range than 

 those employed for most other parts of 

 the body. The difficulty experienced 

 in obtaining fresh and normal adult 

 specimens has turned investigation 

 toward human fetuses and the ears of 

 experimental animals. 



The commonly used fixatives are 

 either Zenker's fluid, with or without 

 acetic acid, Zenker-formol, 10% forma- 

 lin, Wittmaack's solution and Heiden- 

 hain-Susa. Mygind, S. H. and cowork- 

 ers (Acta oto-laryng., 1945, 33, 273- 

 280) prefer the Wittmaack's for fixation 

 of hair cells and use the latter for 

 study of such structures as the stria 

 vascularis. The best results are to be 

 obtained by the use of animal material 

 for which prompt fixation by perfusion 

 methods has been done. Kristensen, 

 H. K. (Acta oto-laryng., 1945, 33. 225- 

 244) recommends the use of a 6% gum 

 arable in physiologic saline for intravital 

 perfusion to precede the fixative. Iso- 

 lated temporal bones placed in fixative 

 are prone to show autolytic changes 

 in end organs and ganglion cells in 

 one-half hour following death. The lit- 

 erature is filled with autolytic changes 

 described as specific pathologic altera- 

 tions due to drugs, toxins, poisons, and 

 so forth. Actually many of these are 

 the result of poor penetration of fixa- 

 tives and elapse of time between au- 

 topsy and fixation. In an attempt to 

 overcome the slow penetration of a fixa- 

 tive and prevention of artefacts Guild 

 made use of water from which gases 

 had been exhausted as the medium for 

 fixatives, decalcifying solutions and al- 

 cohols. 



A variety of decalcificants have been 

 used with the view to preserving finer 

 cell structures of the soft tissues, viz: 

 Formic, trichloracetic, and trichlora- 

 lactic acids, long immersion in MuUers' 

 fluid and so forth. Nitric acid in 2 to 

 5% concentration is generally used for 

 human temporal bones. The lower con- 



