. General physiology; an outline of the science of life. 108 GENERAL PHYSIOLOGY drop. At the surface of the latter the tannin is united with the gelatine, and thus the continual apposition of new layers leads to the thickening of th(.' membrane. The water, however, presses into the interior of the drop, so that this constantly swells and increases in size. By this pi'ocess there api)ear continually in the precipitation-membrane extremely fine holes and cracks ; these, however, become closed by new precipitate at the pioment of their ajipearance. Thus, the artificial c(;ll grows continually and
. General physiology; an outline of the science of life. 108 GENERAL PHYSIOLOGY drop. At the surface of the latter the tannin is united with the gelatine, and thus the continual apposition of new layers leads to the thickening of th(.' membrane. The water, however, presses into the interior of the drop, so that this constantly swells and increases in size. By this pi'ocess there api)ear continually in the precipitation-membrane extremely fine holes and cracks ; these, however, become closed by new precipitate at the pioment of their ajipearance. Thus, the artificial c(;ll grows continually and uniformly larger until all the gelatine is m combination. The formation and growth of tht; membrane, which in the large drop take i)lace relatively rajiidly, proceed very gradually in the small living cell. In botany a fruitless discussion has been going on for a long time over the question whether the cellulose-membrane of the plant-cell is formed by intussuscep- iion, , bythe deposition of new particles between the old ones, or by apposition, , by the deiDosition of particles upon the outside.^ This discussion arose in connection with Nageli's unha])])y com- jmrison of, or rather distinction between, growth in crystals and growth in organ- isms. Latel}' the view has been gradu- ally accepted that both modes lead to the growth of the membrane—the one to growth in surface, the other to growth in thickness. If the protoplasmic body of the cell itself is enlarged, the membrane is extended. In the process, as a rule, no actual cracks appear, as in the artificial eel!, but as a result of the extension the spaces between the single particles of the membrane become wider and larger, so that new particles of protoplasm can enter in. But, on the other hand, the stratification of the membrane ])arallel to the surface, which is visible under high magnifying p(jwers and with increasing thickness becomes constantly more distinct, shows that increase in thickness by apposition is
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