Experimental Physiology

Experimental physiology has little to do with kites. And this is not Benjamin Franklin’s kite. That kite was flown in June of 1752. Nothing special, as kites go. But it is characteristic of the great scientific breakthroughs of the 18th century.

Benjamin Franklin and Albrecht Haller start off the 18th century’s renewed interest in science. It was a century of many new discoveries, and the foundations for the boom in scientific investigation characteristic of the 19th century.

Benjamin Franklin (1705, or 06, to 1790) was an active participant in many fields of endeavor. Somewhere in a busy life of signing the Declaration of Independence, being the first Postmaster of the United States, and inventing lightening rods, bifocals and stoves, Franklin managed to pursue his interests in science.

In his day, it was not clear what electricity is, or where it comes from. Many believed in the human spirit, and animal spirits, as causal forces. You can wiggle fingers on each hand because the human spirit rushed around the body animating movement.

At a time when research was uncommon, Franklin was an advocate of systematic thinking and experimentation. Over 100 years before Wundt, Benjamin Franklin

There had been others with an interest in science before Franklin but the 18th century was the start of new frontiers in science in general, and physiology in particular.

Another early 18th century scientist, Albrecht Haller (1708-1777) was a Swiss botanist, naturalist an physiologist. He is best know for demonstrating that nerve impulses and muscle contractions are not the same thing. Consequently, he is called the father of modern physiology.

Nerves

Continuing the theme of nerves and electricity, Galvani, Volta and Humbolt converged on the same topic. Born and educated in Bolgna, Italy, Luigi Galvani (1737-1798) is less known as a professor of anatomy than for his conclusion that animal tissue is capable of generating electricity. Using an electrically-charged scalpel, he accidentally touched the probe to the leg of a frog, causing it to twitch. Galvani did not conclude that tissue conducts electricity but that animals actually generate it themselves.

Alessandro Volta (1745-1827) was also Italian but in contrast to Galvani, Volta did not believe in animal electricity. He maintained that the flow of electricity was between two metals Galvani had placed on either side of the frog’s leg. The frog was simply a detector (a conductor) of the electricity. A professor of physics, Volta built the first electrophorus (electrostatic generator) and the first electric battery. He experimented with igniting gasses using an electric spark, and with animal electricity.

The issue of animal electricity was resolved by German naturalist Alexander Friedrich Wilhelm Heinrich von Humboldt (1769-1859). He concluded that Galvani’s animal electricity and Volta’s bimetallic electricity were related phenomenon. Animals do produce electricity (e.g., nerve conduction) but that does not rule out the production of electricity using metallic materials. Humbolt is also known for his exploration of Latin America, including Venezuela, Columbia, the Andes Mountains of Ecuador, and the Orinoco and Amazon river systems.

In contrast the thinking of his day, Johannes Muller (1801-1858) held that each nerve leads to one sensation only. The message nerves carry is not determined by the stimulation (visual, auditory or tactile) but by the brain. If the eye is stimulated by touch (pressure), electricity or by light waves, the result is a visual sensation. Muller proposed that perception is in the nerve. His Doctrine of Specific Nerve Energies states that vision nerves, touch nerves and hear nerves have unique qualities specific to that nerve. Vision nerves can only carry visual signals. The starting point doesn’t matter and the ending point doesn’t matter. The nerve itself if special. It took nearly 90 years for researchers to show that all neurons work the same.

Charles Bell and Francois Magendie show you don’t have to like each other to make scientific discoveries. The issue was how nerves worked. No one really knew. A common belief was that nerves for a specific sense had unique characteristics. Hearing nerves were fundamentally different from vision nerves. The senses were so different that the underlying processes must be different too, obviously.

Nerves were also thought to be bidirectional. There was no need for two systems when one system would do. Scottish surgeon Charles Bell (1774-1842) was the first to show there are separate systems for sensory and motor information. Using dissection, he showed that motor neurons go up the anterior side of the spine. Motor and sensory neurons are not bidirectional. Motor neurons go out of the spine and activate muscles. Sensory information goes into the spine, and up to the brain. Bell was also among the first to show that different parts of the brain held different functions.

Using dissection, Bell could only show motor neurons are separate from sensory neurons, and they come down the anterior side of the spine. A dead animal can’t demonstrate sensory acquisition. Eleven years after Bell, French physiologist Francois Magendie (1783-1855) used vivisection to demonstrate how sensory nerves work, and that they go up the back of the spine.

Magnelie’s work and claims of discovery were highly contested. He operated on live animals, often quite cruelly. He reportedly nailed one dog to a table by its paws and ears, uncovered the nerves on one side of the face, and left it overnight so it continue his demonstration the next day. Check Wikipedia is you want more blood and gore.

A theoretical fight between Bell and Magnelie became a war between the UK and France over animal cruelty. The French tended to think it was just a dog. The UK past one of its first laws against animal cruelty.

The question of unique nerves versus all nerves are alike was settled by German physiologist Johannes Muller (1801-1858). Müller’s theory of specific nerve energies argued that all nerves are the same. Like trains they can carry different information but the differences are specific to the nerve’s content, not to the outside world. A vision nerve is unique in its route, not in its anatomical properties.

To be fair, I invented the train analogy but I’m sure Müller would have used it, if he had thought of it.

Physiology to the rescue

A small example, then a big one.

The philosopher Rene Descartes (1596-1660) had proposed a dualist explanation of behavior. He said reflexes and autonomic responses were the work of the body. Voluntary behavior was the work of the soul. Of course this was all theoretical.

It was up to the Scottish physician Marshall Hall (1790-1857) to experimentally differentiate between reflexes and learned behavior. He showed that voluntary, conscious movements were controlled by the higher brain stem and that involuntary, unconscious movements were controlled by the lower brain stem.

A much bigger controversy was settled, for most people, by French physiologist Jean Pierre Flourens (1794-1867). The problem was phrenology. The solution was ablation.

‘Yes, some animals were killed in the process but they were rabbits and frogs, not dogs. And they were not in pain.

Franz Gall (1758-1828) was a good combative anatomist and a poor a poor physiologist. He compared skulls of various animals, after death. He filled each skull with shot (think muskets here), and counted the number it held. It was a good dependent variable (number is shot) and a good independent variable (skull size). It didn’t account for what was in the skull but did provide an approximation of brain size.

Gall found bigger animals had bigger skulls, and presumably, bigger brains. He concluded larger species are smarter than smaller ones.

Franz Gall

This conclusion turned out to be somewhat true. Brain size is a quick and gross rule of thumb. The rule holds, except at the extremes. There is a minimum size required to do anything really intelligent. And a maximum beyond which bigger isn’t better. Elephants are very intelligent but they could do with smaller brains if they had a better circulatory system. They have such huge skins a lot of brain power is dedicated to maintaining temperature control. They are smarter than dogs, which are smarter than rabbits, which are smarter than frogs, which are smarter than flies.

Gall’s big contribution to history was phrenology. He believed the brain has multiple, separate functions, it is not one organ doing everything. So far, true.

Gall thought an ability would make one portion of the brain larger than the others (somewhat true) and that you could detect these regions by the bumps on the head (not true). The idea was that the brain is like a muscle (not true), and that as an area grew it would push up against the skull (not true) and make the skull have a bump (not true).

Phrenology wasn’t true but it was popular. For over 100 years, people believed you could discover and diagnose personality, intelligence and moral fidelity by the size of the nose, narrow set of the eyes, and color of the skin. Darwin almost didn’t get to go on his voyage because the ship’s captain thought he looked lazy.

Phrenology had become so accepted in the general population that the scientific community was concerned. The lauded benefits of phrenology reached Napoleon Bonaparte (1769-1821), who commissioned the top scientists to find out the truth. The Academy of Sciences of Paris didn’t want to do it so they gave the job young researcher.

French physiologist Jean Pierre Flourens (1794-1867) was a pioneer in the use of anesthesia. He showed that chloroform could be very effectively used on animals and people. He also is known for his studies of bone formation.

Flourens was a strong advocate of using experimental methodology. Using ablation and systematic observation, Flourens showed that Gall was partially correct; the brain does have different areas of function. Perfecting the technique on pigeons, Flourens removed portions of the brain and observed the effects. His extirpation procedure (destroying small parts of the brain) revealed that each part of the nervous system had its own function and acted as a unit. Removal of the cerebral hemispheres resulted in loss of perception and judgment. Removal of the cerebellum caused loss of equilibrium and an inability to coordinate motor movements. Removal of the brainstem resulted in death.

Another problem physiologists were challenged with is still not fully explained. The issue is how the objective external world is represented in internal subjective processes.

As a pioneer of experimental psychophysics, Ernest H. Weber ( 1795-1878) noted that the skin registers changes in temperature, not constant readings. Similarly, he showed that if 2 pin points are placed close enough together, they are perceived as one pin prick. Weber had subjects hold weights in each hand and report whether they were identical or different. He found that people could not detect a change in weight until there was a 1:40 ratio. Weber’s jnd (just noticeable difference) was the first reliable law of psychophysics.

A student of Weber, Gustav Theodore Fechner (1801-1887) wrote Weber’s idea in the form of a formula, and called it Weber’s Law. He revised Weber’s law (showing it was logarithmic), and continued Weber’s work on jnd (just noticeable difference), applying it to weight, temperature, etc.

Fechner’s accomplishments are not limited to expanding on Weber’s insights. He studied afterimages and color vision. His description of the “pleasure principle ” influenced Freud years later.

And he solved one of life “insoluble” questions. Although philosophers had struggled to determine how the mind and body interrelate, Fechner proposed an elegant solution to the problem. On October 22, 1850, Fechner had a sudden burst of insight. He saw a quantitative relationship between stimulus (the mind) and sensation (the body). Sensation is dependent on stimulation but they increase at different rates. An increase in sensation requires a geometrical increase in stimulation.

Contemporaries

Wundt was one of several students who made major contributions to science. Before Wundt there was Bois-Reymond and Helmholtz. Emil du Bois-Reymond (1818-1896) became known for his work in bio electricity. His studies on animal electricity became quite well known. His friend Hermann Helmholtz (1821-1894) became even more famous.

The major accomplishment of Helmholtz was measuring the speed of the human spirit. In contrast to Descartes’ view of nerves as hollow tubes the human spirit travels through, Helmholtz believed in nerve impulses.

Measuring the speed of a nerve was thought to be impossible. The human spirit was thought to be too fast to measure. It was thought to travel instantaneously. Clearly, you can’t capture or measure a spirit.

Helmholtz built a mechanism to measure the speed of a neuron. He was also lucky. Some never sees travel really fast. The one Helmholtz chose was relatively slow. Still, it quite astonishing as a young researcher to do something no one thought possible. In is not surprising he achieved worldwide fame quite suddenly.

Helmholtz also revived Thomas Young’s theory of color vision, invented the ophthalmoscope (an instrument used to look into the eye and examine the retina, and showed that the ear’s basilar membrane vibrates sympathetically to stimulation.

French physician Paul Broca (1824-1880) is best known for his discovery that the brain has a specific area responsible for speech. Broca hypothesized that his patient’s aphasia was caused by a brain lesion. After the patient died (of unrelated causes), Broca performed an autopsy and found a lesion on the third frontal convolution of the left cerebral hemisphere. This portion of the brain which controls speech is called “Broca’s area” More of a clinician than experimenter, Broca taught surgical pathology in Paris, founded a society of physical anthropology, and served in the French Senate.

Wundt

These are the experimental researchers leading up to Wundt. He took their techniques and findings, combined them with his philosophical predecessors, and created a new science: psychology.