CELL STRUCTURE 45 



of some of the cell structures, although it is by no means certain that the conclu- 

 sions drawn will all be verified. In the nucleolus he finds a substance resembling 

 glol)uliu, the i^runuloplasiu of tlic cell body lie rej^ards as an albumose, the spongio- 

 plasni as histone, mast cell granules as mucin or mucoid substances. Nissl bodies 

 he holds to be albumose, altho otiiers have beUeved them to be nucleins." 



The Cell-wall** 



The cell membrane in most animal cells is inconspicuous struc- 

 turally, but in discussing osmosis it was shown that it is of the greatest 

 biological importance. There is no direct chemical or microscopical 

 evidence at hand showing the composition of the animal cell mem- 

 brane, but by observations on its behavior when the cells are in solu- 

 tions of different sorts, facts have been collected indicating that 

 phospholipins and cholesterol, and probabl}^ alhed fat -like bodies, are 

 prominent constituents. The substances that difTuse through most 

 cell walls are just the substances that are soluble in or dissolve these 

 lipoids, e. g., alcohol, chloroform, ether, etc., and it is probable that 

 the anesthetic effects of many of these substances depend in some way 

 on their fat-dissolving power and the large proportion of lipoids in 

 nerve-cells. These observations were made first by Overton^^ and 

 Meyer, ^"^ and led to the now prominent but disputed hypothesis that the 

 permeability of cells is determined by the lipoids. Of particular in- 

 terest for our purpose are Overton's observations on the effects of dyes 

 on living cells. The best known vital stains (z. e., stains that will 

 enter the living cell without requiring or causing injury to it) are neu- 

 tral red, methylene blue, toluidin blue, thionin, and safranin. If 

 uninjured cells, e. g., frog eggs, are placed in watery solutions of these 

 dyes they soon become filled with the coloring-matter, which seems to 

 penetrate the cell menbrane quite uniformly at all points; if the dyed 

 eggs are then placed in clear water, the stain diffuses out again, showing 

 it to be simply absorbed, rather than chemicallj^ combined. In 

 contrast to these stains the sulphonic acid dyes, such as indigo car- 

 mine and water-soluble indulin, nigrosin, and anilin blue, do not pene- 

 trate the living cell at all. Overton tested the solubilit j^ of dyes which 

 are not vital stains and found them all insoluble in oils, fats, and fatty 

 acids; but the dyes staining living cells were readily soluble in lecithin, 

 cholesterol, "protagon," and cerebrin, the so-called cell lipoids. Fur- 

 thermore, if crumbs of lecithin, "protagon," or cerebrin were placed 

 in very dilute watery solutions of these dyes, they were found to absorb 

 from the water the vital stains, but not the others, which indicates 

 that stains that penetrate living cells are more soluble in lipoids than 

 they are in water. 



" See Unna, Berl. klin. Woch., 1914 (51), 444; Muhlmann, Arch. mikr. Anat., 

 1914 (85^ ,361. 



•** See Zangger, "Ueber Membranen und Membranenfunktionen," Ergebnisse d. 

 Physiol., 1908 (7), 99; also R. S. Lillie, "The Role of Membranes in Cell Pro- 

 cesses," Popular ScienceMonthlv, Feb., 1913. 



" Jahrb. f. wissentschaftl. Botanik, 1900 (34), 669. 



" Arch. f. exp. Path. u. Pharm., 1899 (42), 109. 



