We knew next to nothing about neurons until the mid 19th century only because we did not have the technology to be able to clearly see neurons beneath the microscope. Three things needed advancement in order for us to be able to examine neurons: Microscopes, Staining techniques, and hardening techniques (Finger, 2000).
Robert Hooke and Anton Van Leeuwenhoek were two 17th century scientists that greatly improved the microscope. Hooke is known for looking through the microscope and commenting that the what he saw looked like a bunch of miniature prison cells. That is actually where the term “cell” for “cells” comes from (Finger, 2000).
Click here to see how microscopes have developed over the ages
Today we have scanning electron microscopes which are powerful enough for us to see up to 100,000 times our normal sight! In comparison, light microscopes, like the ones you used in biology class back in high school, only allow you to see up to 2,000 times your normal sight (Scanning Electron, 2009).
Ernest Ruska and Max Knoll co-created the first electron microscope in 1931 (Ruska, 1986), and it was in the 1950s that the electron microscope finally allowed scientists to witness once and for all that synapses exist (Sheperd, 1994).
It is necessary to harden specimens so that you are then able to cut thin enough slices to place on the slide. Techniques for hardening specimens was developed in the 19th century (Ochs, 1965). Different techniques have been applied throughout the ages, such as boiling the specimen in oil, and soaking it in alcohol. Today formaldehyde is commonly used by scientists (Finger, 2010).
Without proper staining techniques, one would be unable to have a clear enough view of the specimen against the background. One of the first major stains was the carmine stain which came out around the 1860s. This stain actually comes from insects. It is a reddish material produced before particular insects lay their eggs (Finger, 2000).
It was the Caramine stain that allowed us to get our first close look at neurons, for in 1865 Otto Friedrich Karl Deiters’ observations of neurons were published (Finger, 2000). He appropriately pointed out the Soma, or body, of each nerve cell, as well as their dendrites.
- The next major stain was produced in 1873 by Camillo Golgi which has become known as the silver stain because one of the ingredients is silver nitrate. Interestingly he did not invent the stain in a fancy laboratory, but in a small lab within the kitchen of his apartment. The process for creating the silver stain is quite meticulous:
The procedure was as follows. Blocks of freshly removed nervous tissue were hardened and fixed in an aqueous solution of potassium dichromate (2.5%) for 1 to 45 days (sometimes even longer) and then left for variable periods in a solution of silver nitrate (0.5 to 1%). Next, the blocks were dehydrated and cut without embedding; the sections, which were generally very thick (100 m or more), were cleared in turpentine, attached to slides and covered with gum damar without using coverslips. In order to observe the sections from both sides, Golgi mounted them on a coverslip which he positioned over the aperture of a hollowed-out wooden slide. (Pannese, 1999, pp. 133)
What is so fascinating about Golgi’s silver stain is that it creates what has become known as “the black reaction.” Only about 1-5% of the nerve cells actually get tainted black against the yellowish background. This is good because if all the nerve cells were stained, then one would not see anything besides a big blob underneath the microscope. Scientist only have theories about why the black reaction occurs, but no one knows for certain (Pannese, 1999).
Golgi’s silver stain was a major breakthrough, but it was not perfect. Cajal later improved the silver staining technique by cutting thicker slices of the specimen, staining more heavily, and only staining samples from birds or young mammels because their myelin sheaths were not as fatty which produced better slides (Finger, 2000)
Finger, S. (2000). Minds Behind the Brain: A History of the Pioneers and Their Discoveries. New York NY: Oxford Press.
Ochs, S. (1965). Elements of Neurophysiology. New York, NY: John Wiley & Sons. Inc.
Pannese, E. (1999). The Golgi Stain: Invention, Diffusion and Impact on Neurosciences. Journal of the History of the Neurosciences, 8(2), 132-140. Retrieved from Academic Search Complete database.
Ruska, E (1986). Autobiography In Nobelprize.org. Retrieved November 5, 2010 from http://nobelprize.org/nobel_prizes/physics/laureates/1986/ruska.html
Scanning Electron Microscope -SEM. (stressEngineering). (2009). [YouTube]. Available from http://www.youtube.com/watch?v=KYNknR-e5IU&feature=player_embedded
Shepherd, G. M. (1994). Neurobiology. New York, NY: Oxford University Press.
This page was created by Neil Thorne