If the organism is a whole and each section of it functions normally within that whole, then in the analytic experiment, which isolates the sections as it studies them, the properties and functions of any part must be modified by their isolation from the whole of the organism.
Thus, they cannot reveal the function of these parts in normal life.
There are innumerable facts which demonstrate how the functioning of a field is changed by its isolation. If we want to use the results of such experiments for understanding the activity of the organism in normal life (that is, as a whole), we must know in what way the condition of isolation modifies the functioning, and we must take these modifications into account.
We have every reason to occupy ourselves very carefully with this condition of isolation.”
Kurt Goldstein (1878 - 1965) from The Organism.
Goldstein was a neurologist and philosopher.
Above, Goldstein is trying to show that dissecting something - whether an animal or an idea, and isolating one aspect of it (examining the evolution of an animal by consider how a certain part of its body evolved, for example. or pulling the DNA out of a mouse to learn about mouse genetics) disrupts the very thing we seek to study and learn about - the whole organism or the whole phenomenon.
To pull a petal off a flower creates a dead petal. We can study it, but we must be cognizant that it is not a part of the dynamic whole of the flower anymore. So we must at the same time observe how the isolation changes the subject we’re studying at the same time as studying the subject itself.