. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter XIII —143— Vital Staining minutes, the liquid was centrifuged, the sediment examined under the microscope and the concentration of the dye in the liquid measured by the colorimeter. It was thus possible to plot in terms of pU the quantity of dye retained by the yeast. A study of the curves showed that the lower limit of pU at which accumu- lation of neutral red begins is much lower than 7. It is at pB. But at that point the staining of the vacuole is too weak to be visible under the microscope and only the mea
. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter XIII —143— Vital Staining minutes, the liquid was centrifuged, the sediment examined under the microscope and the concentration of the dye in the liquid measured by the colorimeter. It was thus possible to plot in terms of pU the quantity of dye retained by the yeast. A study of the curves showed that the lower limit of pU at which accumu- lation of neutral red begins is much lower than 7. It is at pB. But at that point the staining of the vacuole is too weak to be visible under the microscope and only the measurements give evidence of the absorption of the dye. This is appreciable only beginning with a pU of From a value of , the absorption gradually increases and the curve rises to a maximum at pR From this point the curve descends. The quantity of neutral red absorbed at the maximum pB. value is found to be g. for Amount absorbed in grs. per cent of fresh yeast. g. of yeast (suspended in a 100 solution), which gives a con- centration of g. of neutral red for 100. g. of fresh yeast. In the experiment with cresyl blue the lower limit at which accumulation of the dye begins is also at pH but the curve does not redescend until about pH. 10. The maximum quantity of cresyl blue absorbed is g. for g. of yeast which makes a concentration of 1 g. of cresyl blue for 100 g. of fresh yeast. The curve for Nile blue is very different, for the lower limit is at pK (absorption begins in a very acid medium) and steadily in- creases to pK 10, at which point the curve flattens out. The maxi- mum quantity of Nile blue absorbed by g. of yeast in the presence of g. of Nile blue is g. which makes a con- centration of dye of 3 g. for 100 g. of fresh yeast. These rather disconcerting results demand explanations. Two facts are indeed surprising: first the descending portion of the curve for neutral red after the maximum pK value is r
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