Soru

Passage:
In the late nineteenth century, neuroanatomy was dominated by the reticular theory, championed by the Italian pathologist Camillo Golgi, which posited that the central nervous system comprised a continuous, syncytial network of physically anastomosed nerve fibers rather than discrete cellular entities. Golgi supported this conception through his revolutionary histological technique developed in 1873—the reazione nera, or "black reaction"—which utilized potassium dichromate followed by silver nitrate to precipitate silver chromate within neural tissue. Paradoxically, while the black reaction stained only a minute fraction (typically one to three percent) of neurons in any given preparation, it impregnated those few cells in their entirety, revealing intricate arborizations of axons and dendrites against a transparent background with unprecedented clarity. Despite this sparse labeling, Golgi interpreted the microscopic labyrinth as empirical confirmation that axonal branches fused seamlessly into an unbroken, diffuse reticular web responsible for holistic nervous transmission.

The Spanish neuroanatomist Santiago Ramón y Cajal, however, seized upon Golgi’s own staining method in 1887 to mount a decisive challenge against the reticular consensus. By modifying the immersion duration and applying the black reaction to embryonic and neonatal avian and mammalian specimens—whose less developed myelin sheaths facilitated deeper and more uniform chemical penetration—Cajal observed that axonal terminals consistently ended in free, unattached extremities rather than continuous fusions. These free endings terminated in close contiguity with, but clear structural separation from, the dendrites and perikarya of adjacent nerve cells. Cajal’s meticulous observations formed the empirical bedrock of what the German anatomist Wilhelm von Waldeyer-Hartz formally designated in 1891 as the "neuron doctrine," which held that the individual neuron is the fundamental genetic, structural, and functional unit of the nervous system.

Crucially, Cajal did not claim that contiguous communication occurred without structural specialization; rather, he explicitly documented that the microscopic gaps between terminal arborizations and receptive cell bodies precluded cytoplasmic continuity, necessitating polarized transmission across distinct functional junctions. Furthermore, while Golgi maintained that dendrites functioned exclusively as nutritive conduits absorbing nutrients from adjacent glia and blood vessels, Cajal demonstrated that dendrites actively participated in receptive conduction, receiving impulses directly from axonal arborizations. Golgi steadfastly rejected these findings until his death, utilizing his 1906 Nobel Prize lecture to reiterate his adherence to a continuous syncytium, yet Cajal’s modified silver preparations decisively redirected the trajectory of modern neurobiology by establishing the cellular autonomy of the neuron.

According to the passage, Cajal applied the black reaction staining technique to embryonic and neonatal specimens primarily because