Figure and Form

Cajal's family in 1894. This photo was included in his autobiography (1). Interestingly Cajal only names one of his children in his autobiography, Enriqueta, who died from tuberculosis. He would lose another one of his daughters to meningitis and a son to heart disease before Cajal himself passed away.

Cajal's scientific work and private life were intertwined with one another, unable to be separated from the other. By 1885, Cajal was married with two children and expecting another while also living through a cholera epidemic sweeping through the Spanish region of Valencia. Cajal describes his life as such:

"My family had increased with two children and another was about to be born to me. It is seen, then, that the children of the flesh and the children of the spirit emerged at the same time. But the latter never harmed the former. If each newborn brings under his arm, according to the common saying, a loaf, each published monograph provided, with the noble satisfactions of the spirit, the material bread of existence. They gave me a reputation as a worker and scholar... and contributed to sustaining and raising the credit of my modest Academy of Anatomy and Histology. They, in short, with my subsequent books, later earned me valuable sympathy and approval in Madrid." (1)

Cajal makes use of a Spanish colloquialism that, when translated literally, is "Every baby is born with a loaf of bread under his arm." This phrase essentially means that a newborn brings joy and good fortune to a family. Other things that brought Cajal good fortune during this time were his publications. Cajal gained not only a good reputation among Spanish physicians and scientists, but also notoriety, approval, and satisfaction.

Cajal began his studies of neurodevelopmenT and Neuroembryology around 1890, what he called neurogenics. (1)

Cajal studied neurodevelopment in several species, including chickens, rabbits, mice, and humans (4). For embryonic studies, he often made use of chick embryos. During this time period, it was unclear how exactly neurons themselves grew from immature neuroblasts to fully mature neurons. There were several competing theories by prominent neuroscientists of the time.

Victor Hensen's Hypothesis

Catenary Hypothesis

Wilhelm His' and Cajal's Hypothesis

The schematics of the three main competing hypothesis of neuron development above were drawn by Cajal (1).

Neuroscientist Victor Hensen believed neuron growth was accomplished by stretching and strengthening of connections. Similar to the Reticular Theory, Hensen believed that neurons were connected to one another through cytoplasmic bridges creating a network of webbing (20). These bridges would stretch out over time as neurons migrated away from each other during development (1).

The Catenary Hypothesis-- catenary meaning 'does not stretch'-- was created in opposition to Hensen's model. It was supported by several neuroscientists at the time. In this model, several neuroblasts fuse to form one mature neuron (1).

Supported by the work of neuroscientist Wilhelm His, Cajal put forth a third theory (1). A neuroblast sends out a projection that ends in a growth cone. When the growth cone reaches its target, the cell undergoes final differentiation into a mature neuron.

Where did Hensen's theory and the Catenary Hypothesis go wrong?

At the time Hensen proposed his theory, in 1864, Cajal was only 12 years old (20). Neither the Reticulary Theory nor Cajal's Neuron Doctrine had been proposed yet, meaning that Hensen was essentially postulating on how neurons develop connections without even knowing how they connected.

The Catenary Hypothesis' errors are more difficult to explain. Perhaps observations on developing peripheral neurons, revealing myelination mediated by Schwann cells, led to incorrect conclusions.

Nonetheless, this example shows Cajal's capabilities when he collaborated with other scientists. Though rare in his research, as he valued his intellectual and financial independence from others (1), Cajal and His were together able to deduce the correct method of cellular neurodevelopment.

Nationalism &
Pr-eye-de

Cajal had great pride In his country, and even more for Spanish Science itself.

So when Spain lost the Spanish-American War in 1898, Cajal reports struggling with his ability to work (1). He blamed the war, and the subsequent loss, on scheming industrialists, selfish politicians, and a lack of national identity. He did, however, produce findings regarding the structure of the optic nerves.

Lower vertebrate panoramic vision without optic nerve crossing. (1)

Lower vertebrate panoramic vision with optic nerve crossing. (1)

Mammalian binocular vision with optic nerve crossing. (1)

Human binocular vision in Neuroscience

Necessity of the Chiasm

Cajal's diagrams above show the necessity of optic nerve crossing in order to transmit the correct image to the brain. The best way to interpret these images is to compare the form of the arrow the eyes are viewing (top of the diagrams) with the arrow reproduced in the visual centers of the brain (middle and bottom of the diagrams).

The first two images show visual processing in lower invertebrates, such as lizards and fish. Because their eyes are on opposite sides of their head, they had panoramic vision. The left-most image shows the image that would be produced given that no crossing occurs. Note that the image of the arrow is mirrored but also in the wrong order. Without crossing, the arrow head points to its tail. When crossing of the optic nerves is added, the image produced is still mirrored but is now recreated in the correct order.

Humans' eyes face forwards, creating binocular vision. As Neuroscience shows, the visual fields of parts of the eye overlap with one another, creating redundancy but also a sharper image in the center of the visual field. Cajal shows the exact same layout of Neuroscience's representation of the visual field, complete with the parts of the optic nerve that do not cross over at the optic chiasm.

Cajal also supersedes Neuroscience in the information it conveys. Notice in the middle two images that Cajal illustrates the neurons included in the visual pathways, rather than just depicting them as colored lines. This puts the visual pathway into context, not just as something theoretical, but as something constructed by the body's neurons.

"Not with hollow declamations, which claim to be patriotic and turn out to be boasts of ignorant chauvinism, but with positive and indisputable facts I have demonstrated the aptitude of the Hispanic people for scientific research. The alleged incapacity of the Spanish for anything that is not a product of fantasy or artistic creation has been reduced to a vulgar cliché."

- Santiago Ramón y Cajal (1)

In light of what Cajal wrote above, it is unfortunate that Cajal's science is often reduced to just art.

Art critics have described Cajal's illustrations as “graceful anemones,” “meandering spiders,” “fractal branches of fairy-tale trees,” and “neuronal wildlife" (7). His work has been compared to “a fantastic netherworld of floating forms, linear networks, bristling nodes and torrential energies" and an “immense cosmic universe” (11). These interpretations emphasize the fantastic and dream-like nature of Cajal's work. What some critics fail to account for is that these drawings were scientific findings first and art later.

Imagery

Cajal used imagery to argue for his theories and along the way created works appreciated as art.

This use of imagery continues to shape science communication and learning today.

The images above help to demonstrate the variety of forms that imagery can take. They depict astrocytes, a common non-neuronal cell type in the brain. The left image shows a histological slide produced by Cajal, and the middle image shows his illustration of astrocytes based on the slide (4). Their end feet stretch to a capillary within the brain, controlling the blood-brain barrier. The rightmost image shows Neuroscience's diagram of an astrocyte.

Both Cajal and Purves emphasize the spindly projections of astrocytes, thus giving them their name roughly translated from latin: star cells. But other than these appendages, Cajal's astrocytes look nothing like Neuroscience's. Why might this be?

The Answer?
MImetic and Didactic Imagery

Mimetic imagery shows subjects as they are, showing off individual forms even if they deviate from the norm (18). In this case, a histological slide is the purest form of mimetic imagery. It captures the cells as they are, without an intermediary interpreter.

On the other side of the spectrum is didactic imagery, which aims to reproduce something in its perfect, most representative form (18). Didactic imagery is often used in learning environments, such as textbooks. Neuroscience utilizes diagrams like these to emphasize the parts of an astrocyte's structure that makes it so recognizable, namely its chaotic and branching tendrils.

The histological slide and the textbook diagram have two different goals: to imitate or to teach.

So where do Cajal's illustrations fit into this model? They were one step removed from mimetic imagery, as Cajal did not completely copy his slides. Nor can his images be classified as didactic, as Cajal still demonstrates astrocytes' diversity in form. His illustrations lie somewhere in between, aiming to reproduce what he saw under the microscope while also teaching readers of his publications about the nervous system's structure.

Thankfully for Cajal, some art critics have also considered his work in the context of the wider scientific field, not just in the context of art and art history. One critic writes:

"These small works evoke enough things you already know — landscape, weather systems, trees, marine life — that they bring you back around to reality, implying the multiple purposes if not universality of certain natural structures" (11).

From glial cells and feather stars...

Glial cells via (21). Feather star via (22).