Injury, recovery, and death, in relation to conductivity and permeability . Fig. 85.—Cross section of Ulva lactuca, var. latissima (sea lettuce). (X 450). must decrease its electrical resistance, and vice electrical resistance of the protoplasm may there-fore be regarded as a measure of its permeability to ions. In this connection it should be noted that experiments have beenmade with direct currents. Cf. Stiles and Jorgensen (1914). CONDUCTIVITY AND PERMEABILITY 197 If we attempt to measure the electrical resistance ofthe protoplasm we must first consider the structure ofthe tissue.
Injury, recovery, and death, in relation to conductivity and permeability . Fig. 85.—Cross section of Ulva lactuca, var. latissima (sea lettuce). (X 450). must decrease its electrical resistance, and vice electrical resistance of the protoplasm may there-fore be regarded as a measure of its permeability to ions. In this connection it should be noted that experiments have beenmade with direct currents. Cf. Stiles and Jorgensen (1914). CONDUCTIVITY AND PERMEABILITY 197 If we attempt to measure the electrical resistance ofthe protoplasm we must first consider the structure ofthe tissue. Very useful for experiments on tissues are plantswhich form membranes consisting of a single (Fig. 84)or a double layer (Fig. 85) of cells. In measuringthe conductivity of these plants we obtain much thesame results as with the more complex tissues ofRliodymenia (Fig. 86) and Laminaria (Fig. 87). We. ^^^^©^dS DOOOOOCDCOOC FiQ. 86.—Crosa section of Rhodymenia palmata (dulse). (X 150j. may therefore conclude that the complexity of structureis not a factor of importance in the interpretation of theresults. As a matter of fact in the case of Laminaria theresistance appears to be due cliiefly to the rounded cellslying at and below the surface, while the elongated cellswhich occupy the center of frond have large spacesbetween them through which the current can easily pass. If we consider the structure of the individual cells,we find that in Laminaria (as in the other plants employedin the experiments of the writer) the protoplasm of 198 INJURY, RECOVERY, AND DEATH each cell forms a thin layer, which surrounds a largecentral vacuole filled with cell sap. When tissue (eitherwith or without previous treatment with liquid air) isground with powdered quartz (so open the cells) anda little sea water is added, and the juice is subsequentlyexpressed, it is found to have a little higher
Size: 2041px × 1224px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysiology, bookyear1
