Membrane History - An Introduction to Biological Membranes - page 21

FIGURE 2.6 William Hewson (1739 e 1774). Courtesy of the National Library of Medicine.
must be put in historical context. Schultz's work came only 8 years after Wohler's classic 1828
experiment synthesizing the first organic molecule (urea) by heating an inorganic molecule
(ammonium cyanate). This was the beginning of the end for the theory of 'vitalism', a concept
that believed organic molecules were different from inorganic molecules by possessing
a 'vital spirit' imparted by God. Three years later, in 1839, Theodor Schwann established
the Cell Theory. Incidentally, Schwann's promising career, that included the first use of the
term 'membrane' ended by age 30, as he was ridiculed for having the audacity to suggest
that alcohol fermentation was the result of living organisms. Schultz's use of iodine foreshad-
owed later experiments from the mid to late 19 th century employing vital dyes in the study of
membranes.
Karl von Nageli: (1855)
The botanist Karl von Nageli is usually given credit for laying the foundation for cell
membrane osmotic studies on plant cells ( Figure 2.7 ). Indeed, it is much easier to accurately
measure plasmolysis as a function of external osmotic strength with plant, as opposed to
animal cells due to their thick and easily observable cell walls. Simple microscopic observa-
tions of plasmolysis on thin onion peels (only a few cells thick) are often used in high school
biology classes. In a solution of sufficient salt or sugar, the cytoplasm is observed to pull away
from the cell wall ( Figure 2.8 ). In animal cells the plasma membrane barrier can be clearly
distinguished due to differences in light refraction across the membrane. Light travels
more slowly in the dense cytoplasm than it does in the much less dense bathing solution.