We see it, for example, in the glands; we see it in the skin and we see it in the elements of the nervous system. _Berger_,[51] for instance, established the fact that the ganglion cells of the optic lobe in the cerebrum of newborn dogs only reach their full development when functionally excitated by adequate light stimuli (Figure 9, B), coming from the eye, whereas they remain in the embryonic state when these light stimuli are eliminated. (Figure 9, A.) The cytoplastic increase of volume of the neurons under the influence of functional stimuli is a fact of fundamental importance for the entire happenings of the nervous system and forms the physiological basis for reinforcement of reflexes, which, in its turn, is essential for all acts of memory and intelligence. For the increase in volume of the ganglion cell body is, when functionally activated, accompanied at the same time by an increase of specific capabilities and the intensity of discharge. Its excitation impulses can, therefore, be conducted through a greater number of neurons, with which it is connected, than would be the case if development of the volume of the ganglion cell increased to a less extent. [51] _Berger_: “Experimentell-anatomische Studien über die durch den Mangel optischer Reize veranlassten Entwickelungschemmungen im Occipitallappen des Hundes and der Katze.” Arch. f. Psychiatrie, Bd. 33, 1909. [Illustration: A B Fig. 9. A--Undeveloped ganglia cells in the optic lobe of a dog, the eyes of which have been sewn up immediately after birth. B--Fully developed ganglia cells in the same region of a normal dog of the same age. (After _Berger_.)]