Title: Dissection of a Cow's Eye
Purpose: The purpose of this experiment is to probe the structure of the eye of the cow, and from our observations, to gain a greater appreciation for Goethe's observations concerning color theory.
College-grade dissection kit
Plastic Bad (For disposal)
Image Source: http://johnsonhenryworldschool.blogspot.com
1. Before removing anything from the eye itself, pause to identify significant structure. Note the white, tough sclera, which forms the outer covering of the eye itself, and the rigid optic nerve which provides the brain with the information which forms our sense of sight. The cornea, iris and pupil should also be observable.
2. Cut away the fat and muscle that surrounds the eye. The fat provides the eye with insulation, cushioning from shock, while the muscles allow the organism to actively alter its field of view.
3. Make an incision into the cornea. Note the liquid which is released from the eye upon its puncturing. This is known as the aqueous humor, and lends the eye its globular shape. This is essential to our ability to process light information accurately.
4. Using the scalpel, make an incision into the sclera. Observe how rigid it is, and compare this with your prior thoughts on the structure of the eye. Then use your scissors to cut the eye into two portions. The clear jelly which fills much of the eye is the vitreous humor. It is through this liquid that the eye derives its nutrition.
5. The first portion is the cornea, and is the part of the eye we see in our fellow living members of the Human species on a daily basis. The cornea serves the important role of guarding the internal structure of the eye from external particulate matter. Also, it enables us to accurately observe our environment by bending light which enters the eye.
6. Next observe the pupil. This is done by removing the iris. The pupil is a small hole in the iris which through all light which forms the cow's perception of the world enters. Muscles in the eye contract or relax, altering the shape of the iris, and thus, how much light is allowed to enter through the pupil.
7. Remove the lens, and record your findings concerning its texture, shape, and opacity. Depending on the freshness of the specimen you are dissecting, you may be able to observe the magnifying properties of the lens.
8. So far, we have only investigated the part of the eye containing the cornea. Now, let us direct our attention to the back half of the eye. Inside this half, we find the retina, a film which contains the rod and cone neurons which, through their impulses, inform the brain of what we are looking at. The retina is attached to the back of the eye at a single point, where it forms the optic nerve. This nerve carries signals from the eye all the way to the back of the brain, in humans.
9. The spot where the retina is attached to the back of the eye is known as the blind spot because no cone or rod cells exist there to detect incoming light.
10. Lastly, look behind the retina. One will find the tapetum, a layer of iridescent blue-green film which gives the cow better nighttime vision by reflecting light that enters the eye back at the rod and cones cells, giving them another chance to absorb the light, and process the image.
Observations: See attached Lab Pages
Conclusions: Our dissection of the eye certainly lends support to Goethe's argument that how we view light is not simply inherent of the mechanistic function of light itself, but rather is dependant upon the individual's interpretation of the light, by physiological means. We have seen how the lens magnifies observed light, and also, how the structure of the cornea is important in allowing us to focus light in such a way that it forms recognizable objects for our brain to interpret.
Indeed, the existance of the reflective tapetum in cows, and its absence in humans indicates the structure of the eye plays a key role in how we see. As mentioned in Livingstone's The Biology of Seeing, "our eyes are optimized for acuity rather than for light sensitivity." Cows eyes are constructed to function in light and dark conditions, while our eyes are better in light, but rather deficient in dark situations. So, physiology does play a role in seeing.
However, it is important to note that it is unlikely that Goethe dissected an eye while forming his work on color theory. If he had, he might have been able to elaborate on the 'recovery time' of the eye, and how it varies, in his studies, based on age, after observing the muscles connected to the iris.
Regardless of Goethe's use of dissection to probe the pheonmena he observed, we should be quick to utilize our new knowledge of the structure of the eye to help explain Goethe's color theory. For one, the recovery time he observed was most likely due to the pupil's gradual change in shape as it adjusted for the change in lighting conditions.
The mixing of fringe spectra to create purple and green is most likely a product of the firing of the neurons which detect two different colors. This is then read by our brain as being not two seperate colors in the same place, but rather a mix of them.
Lastly, color imprinting(Seeing the ghost image of a shape of the oppositive color of the shape you where gazing intently at) may be due to a fatiguing of the cone and rod nueral cells that fire for a specific color, which leads to a seemingly stronger impulse for its opposite color when the original color is removed.
Certainly, this experiment has been useful in our investigation of color.