Sniffing for Disease

Anyone who has been to an American hospital has probably noticed its smell. It's hard to describe it exactly, because it's unique, but personally I'd use words such as "sterile," "plasticky," and "nauseating." Clearly I'm not a fan. When I or someone in my household needs to stay home from work because of sickness, I've noticed that there's a smell that hangs around for a couple of days. I chalked it up to simply not showering for a little while.

It turns out there's a lot more to the story than that.

In the days before blood tests and lab results (which is most of human history), doctors had only their senses and logic to treat patients. While most doctors today use sight, hearing, and/or touch to diagnose patients, most of the doctors who came before had to rely on smell and, in some cases, taste as well! In fact, the use of smell as a diagnostic tool goes back thousands of years, and can actually be quite effective.

The Sushruta Samhita is an ancient Sanskrit text that has one of the first mentions of using smell as a tool. In the document, it states: "[B]y the sense of smell we can recognize the peculiar perspiration of many diseases, which has an important bearing on their identification." The history of this document is a fascinating one, and probably deserves its own blog post, but what is clear is that the Sushruta Samhita was written sometime in the middle of the first millennium BCE (though age estimates range from 1000 BCE to 500 CE). This means that the technique of identifying diseases based on smell was probably discovered and passed down through many generations of doctors through oral teachings before it was written down by the original author of the Sushruta Samhita. Later on, more doctors added to its contents, and today it survives as one of only two foundational Hindu texts on the medical profession from ancient India.

From Penn and Potts, 1998. TREE vol. 13, no. 10, pg. 391–396.

When humans began to concentrate more in cities, public health became an important concern for city officials. If a sickness broke out, it could mean the deaths of thousands, if not millions, of people. Bubonic plague, typhoid fever, cholera, and smallpox were (and in some places, still are) serious diseases that kill quickly. If doctors could identify the illness, then they are better able to treat those afflicted and stop the spread of the disease, saving lives. The scent of a patient, especially a strong and unmistakable one, gave doctors the chance to identify the disease quickly. The figure shows the scents of some diseases, though there are quite a few that aren't on the list.

Skip ahead thousands of years to the modern day, and smell is still the defining characteristic of certain illnesses. One disease in particular, called maple syrup urine disease (MSUD), is identified by the unmistakable smell of maple syrup (or fenugreek, if you're not from an area where maple syrup is common). The pleasant smell belies the seriousness of the disease, however. The sweet smell comes from the body's inability to break down long branched chains of amino acids, which causes them to build up to toxic levels in the body. Infants who have this disease initially start out healthy, but then quickly deteriorate. If left untreated, MSUD will lead to permanent brain damage, and in extreme cases, death within a few months. Older adults can develop this disease, and without proper recognition and treatment, may eventually cause the patient's death. If you ever notice that your urine smells like maple syrup, definitely tell your doctor!

Many service animals are trained to alert their charges if they are about to experience an episode or have an attack. Experts think dogs are actually detecting a change in the scent of their charge, as dogs have a much stronger sense of smell than humans do. Some dogs are even trained to sniff out cancer (though their effectiveness at accurately diagnosing cancer has been criticized).

In some cases, smell was not enough, and the doctors actually had to taste the excretions of their patients. This was the most common way for diabetes mellitus (which means "passing through sweet") to be diagnosed--the doctors had to taste their patient's pee! This knowledge was actually fairly well-known even among people outside of the medical profession, as the disease was also called "pissing evil" for centuries.

Today we rely more on technology than scent to tell us about our health and diseases. To be fair, the medical knowledge of medieval Europe certainly got a lot of things wrong, so it's overall a very positive thing that medical practice has changed so much. What hasn't changed is how much humans rely on their senses to explain the world around them. Smell may not be the most glamorous sense, but it was certainly an effective one, and remains an important tool to this day.

Sources:
Brown, R. (1995) What is the role of the immune system in determining individually distinct body odours? Int. J. Immunopharmacol. 17, 655–661.
Liddell, K. (1976) Smell as a diagnostic marker, Postgrad. Med. J. 52, 136–138.
https://www.popsci.com/problem-with-cancer-sniffing-dogs#page-2

Naming a Dinosaur

Most people know about dinosaurs, the “terrible lizards” that dominated the Mesozoic Era from about 252 million years ago until an asteroid hit the Yucatán Peninsula at the end of the Cretaceous period 65 million years ago. At last count there are at least 700 distinct species of dinosaurs discovered and written about in scientific journals. They range in size from the miniscule Compsognathus longipes to the massive (and recently discovered) Dreadnoughtus schrani. Their names often trip the most practiced tongues because of their lengths and their syllabic complexities.

So how do dinosaurs get these names anyway?

First, it’s important to remember that the field of paleontology itself is fairly young; Sir Isaac Newton had invented calculus about 150 years before fossils were recognized as something that belonged to ancient creatures! Even before paleontology emerged as a new scientific field, many people realized that there was something different about these rocks. U.S. President Thomas Jefferson thought the fossils were from animals that could be found elsewhere on the North American continent, so he instructed Lewis and Clark to pick up any fossils they found to bring back. They only found one during their expedition up the Missouri River, but in 1807 and 1808, Jefferson commissioned Clark to collect mastodon bones and teeth, which is now called the Jefferson Collection. It and other fossils are now housed at the Academy of Natural Sciences in Philadelphia, where they are still used for modern scientific study.

Prof. Ted Daeschler (Drexel University) showing off the Jefferson Collection of mastodon bones and teeth at the Academy of Natural Sciences in Philadelphia, PA.

The second thing to remember is that all dinosaurs have two names, according to the Linnaean system of classification devised in the 1750s. The first part of a name is the genus, which is analogous to a surname in English. That first informs the reader what small and specialized group of animals the author is writing about. The second name is their species name, which is the specific animal within that group, analogous to a given name. These names are italicized to note that they are special names, and often the genus name is omitted when talking about multiple species within that group. When that happens, the species name is not capitalized. This is why it is correct to write T. rex, but not T. Rex!

Many of the first dinosaurs described in scientific literature were named simply for their basic  characteristics, translated into either Greek or Latin to distinguish a species name from its description in English. For example, the very first dinosaur described, Megalosaurus bucklandii, literally means “great lizard” in Greek. The second dinosaur described, Iguanodon bernissartensis, simply means “iguana tooth,” reflecting that the first part of its skeleton discovered, the tooth, was initially thought to be from a large iguana. Of course, Tyrannosaurus rex means “tyrant lizard king,” even though recent evidence shows that dinosaurs are likely not lizards at all!

The genus names come from a dinosaur’s general features, but what about the second name? Those are often used to denote the place of the animal’s discovery or where it lived or lives (in the case of extant, or modern, animals). A good example is Velociraptor mongoliensis, which means “swift thief of Mongolia” in Latin.

Another way to name a dinosaur is to honor a paleontologist or another person. For example, Megalosaurus bucklandii is named for William Buckland, Professor of Geology at the University at Oxford and the first scientist to describe Megalosaurus in scientific literature. Today, it is not considered good etiquette to name a dinosaur after yourself, and it is a great honor to have a dinosaur species named after you. Some are named after musicians (Masiakasaurus knopfleri), and some are named after the person who discovered the bones, even if that person didn’t describe them to science (Vectidraco daisymorrisae).

Of course, there are some names that come out of pop culture. Dracorex hogwartsia was discovered by three amateur paleontologists in South Dakota, and was named after the school from the Harry Potter series. Another dinosaur, Zuul crurivastator, is named for the monstrous deity from the original Ghostbusters movie.

New dinosaurs are discovered every year all over the world, so it is possible to one day get the chance to name your own. What would you call yours?

Sources: Behind the Bones documentary: https://www.youtube.com/watch?v=T8wySyiynHk

https://www.rom.on.ca/en/collections-research/research-community-projects/zuul

https://phys.org/news/2006-05-dinosaur-hogwarts-school.html

Paleomagnetism

Our August table’s theme was magnets and electromagnetism. We brought out lots of demonstrations, including a ferrofluid tube, and we had many great interactions with everyone who stopped by our booth. There is one major part of magnetism that we left out, however, so this blog post is dedicated to Earth’s magnetic field. 

While less than 1/100th of the strength of a refrigerator magnet, Earth’s magnetic field is still an important, useful tool. Most of us have used a compass before, so we know that Earth’s magnetic field can be used to find our way. We understand that the magnet inside of the compass will rotate so that the red arrow will always point a certain way. That red arrow is the north part of the magnet, and will always align so that it, indeed, points towards north. It seems trivial: the north part of the magnet points north, and the other end points south. 

Except that it hasn’t always been that way—and it won’t be that way in the future. Using rocks to study how Earth’s magnetic field changed over time is a scientific discipline called paleomagnetism.

The Mid-Atlantic Ridge spans from the Arctic to the Antarctic. It is a series of divergent and transform plate boundaries.

Evidence from the geologic record proves that Earth’s magnetic field has reversed itself many times over Earth’s 4.5 billion year history. Most of this evidence comes from the seafloor in the Atlantic ocean, specifically the Mid-Atlantic Ridge (see picture above). The Mid-Atlantic Ridge stretches from the Arctic to the Antarctic along the bottom of the ocean, and is actually a series of connected divergent plate boundaries (but we’ll get into plate tectonics later). This means that every year, the continents North and South America and Europe and Africa get a little farther away.

At the Mid-Atlantic Ridge, the forces that push the continents apart also send melted rock, magma, up from inside Earth to the ocean floor. This is how new oceanic crust is created, and is some of the youngest rocks on Earth. This deep-ocean crust is also rich in heavy metals, such as iron, because it is formed from magma that comes from inside the Earth, where there is a higher concentration of such elements. Many of these metals are also magnetic. 

While these rocks are still hot, the magnetic dipoles inside of them will act as the needle in a compass does, and align themselves with Earth’s magnetic field. When they cool down to a certain temperature, called the Curie temperature, the rock will maintain the orientation of Earth’s magnetic field. As time passes, more rock is created, pushing the old rock to the side. 

When Earth’s magnetic field switches, the new rocks record an opposite orientation. In the picture below, the black bars represent periods of the current magnetic field's orientation, and white bars represent periods of reversed orientation. Geologists who study paleomagnetism measure the ages of the rocks and the orientation of Earth’s magnetic at the time those rocks cooled. By doing so, geologists piece together the timing of the reversals in Earth’s magnetic field. Their work on rocks from the Atlantic seafloor has revealed that Earth’s magnetic field has reversed orientation many times in the past 180 million years. Curiously, there is no regular pattern to the switches, as they appear to happen rapidly and at irregular times. What causes these reversals is still an open question in geology.

The paleomagnetic record

It is not clear when the next reversal will take place, or how long it will take when it starts to happen. It is an event that has never been observed by humans. Like so many other events in Earth history, the only record we have of this phenomenon is the rocks they left behind. Through geology, scientists discover the history of Earth and how it’s changed, and use it to predict what may happen to Earth in the future. For now, however, simply holding a compass is enough to observe Earth’s magnetic field. 

Sources: http://web.ics.purdue.edu/…/teach…/eas450/paleomagnetism.pdf
http://www.grisda.org/origins/10066.htm
https://www.tes.com/lesso…/QzyoecA6gyWRFw/mid-atlantic-ridge