112 ARRANGEMENT AND STRUCTURE OF SUSTENTACULAE CELLS 



METHODS. 



Kittens, dogs, and rabbits, from birth to 12 days old, white rat fetuses, and 

 young white rats about 2 days old, constituted the material used in these investiga- 

 tions. The isolated cochlea was fixed by trichloracetic acid (5 per cent in water), 

 by Bouin's or by Zenker's fluid, and subjected for many weeks to the mordant action 

 of some drops of iodine in alcohol (70 per cent). Where necessary, after fixation by 

 Bouin's or by Zenker's fluid, decalcification was completed by 2 per cent nitric acid 

 in 70 per cent alcohol. Before embedding in paraffin the pieces were stained with 

 borax carmine and the sections with iron hematoxylin, Congo red, and light green. 



The mitochondria in the sustentacular and hair-cells were fixed in the following 

 manner: Mixture of formalin and bichromate of Regaud (1910), according to the 

 modifications indicated by Cowdry (1916), and subsequent staining with acid 

 f uchsin and methyl-green ; treatment by a 1 per cent aqueous solution of osmic acid 

 for about an hour, followed by immersion in trichloracetic acid, or Bouin's or 

 Zenker's fluid; exposure of the cochlea, the bony wall of which had been previously 

 provided with two or three small openings, to vapors from a 2 per cent aqueous 

 solution of osmic acid for approximately 30 to 60 minutes, and subsequent treat- 

 ment of the piece by one of the three above-mentioned agents; fixation for an hour 

 in a 1 per cent aqueous solution of osmic acid, followed by immersion in a 1 per cent 

 aqueous solution of silver nitrate for 3 hours. By these methods of fixation, and 

 staining with iron hematoxylin and Congo red, the mitochondria can be brought 

 into prominence within one or two turns of the cochlea, occasionally throughout its 

 extent. Osmic vapors have been recommended as a fixing agent for mitochondrial 

 structures by M. R. Lewis and W. H. Lewis (1914). We are able to confirm this 

 statement, having for many years successfully used these vapors, and a subsequent 

 treatment by another reagent, for the purpose of fixing the chondriomites in the 

 ova of the dog. Henneguy (1895) was able to bring into view chondrioconts in the 

 spermatocytes of Helix by the use of osmic vapors. 



The description given herein is illustrated by figures representing three different 

 series of sections: 



(1) Radial, vertical sections of the organ of Corti. These are cross-sections of the 

 rows of hair and supporting cells, the knife cutting the latter along their length and from 

 the axis toward the outer wall of the cochlea (figs. 14, 15, and 16). 



(2) Spiral, vertical sections of the organ of Corti, these being longitudinal sections of 

 the parallel spiral rows, the knife cutting the hair and supporting cells along their length, 

 from the more apical to the more basal part of the spiral organ (figs. 19, 20, 22, and 23). 



(3) Sections tangential and always somewhat oblique to the surface of the organ of 

 Corti, the knife cutting transversely the hair and sustentacular cells of the spiral parallel 

 rows at all levels, from the surface of the epithelium towards the basilar membrane (figs. 

 2 to 13, 17 and 18), so that their arrangement and structure can be traced in cross-sections 

 throughout their lengths (figs. 2 and 3). 



HISTORICAL. 



The structure of the organ of Corti has been exhaustively studied. It is known 

 to be made up of two kinds of cells, the hair-cells and the supporting elements, 



