William Beaumont

I spent last weekend at Mackinac Island in northern Lake Huron. It’s an interesting little place that you reach by ferry and that does not allow any vehicles (except for a few fire engines and ambulances). The ferry ride is dominated by a view of the Mackinac Bridge (the “Mighty Mac”) connecting the upper and lower peninsulas of Michigan. It is a gorgeous piece of engineering (read about its construction in Henry Petroski’s book Engineers of Dreams: Great Bridge Builders and the Spanning of American). On the island, people walk, bike, and ride in horse-drawn carriages. An old 18th century fort dominates the coastline on the south side of the island, and the nearby town has many shops and restaurants (a cynic might call the town a tourist trap). We visited the fort, observed the firing of a civil war-era cannon, had a carriage tour, stopped at “Arch Rock,” and saw the famous Grand Hotel. Last week happened to be their annual Lilac festival, which included a literal “dog and pony show” (the theme this year was board games, and the little terriers carrying big Scrabble pieces on their backs won first prize).

Buying fudge is a Mackinac Island tradition. We stopped at one of the iconic fudge shops, Murdick’s Fudge, and bought a few slabs. One of the Murdick clan, Ryan Murdick, attended Oakland University, where I teach, and obtained a master’s degree in physics. He and I published several papers together, including one about the bidomain model of the electrical properties of cardiac tissue (see Chapter 7 of the 4th edition of Intermediate Physics for Medicine and Biology), one about magnetocardiography (the magnetic field produced by the heart, Chapter 8), and one about how eddy currents induced in electroencephalogram electrodes can influence measurements of the magnetoencephalogram (Chapter 8; the effect on the MEG is very small). The papers are:

Murdick, R. and B. J. Roth (2003) “Magneto-encephalogram Artifacts Caused by Electro-encephalogram Electrodes,” Medical and Biological Engineering and Computing, Volume 41, Pages 203–205.

Murdick, R. A. and B. J. Roth (2004) “A Comparative Model of Two Mechanisms From Which a Magnetic Field Arises in the Heart,” Journal of Applied Physics, Volume 95, Pages 5116–5122.

Roth, B. J., S. G. Patel, and R. A. Murdick (2006) “The Effect of the Cut Surface During Electrical Stimulation of a Cardiac Wedge Preparation,” IEEE Transactions on Biomedical Engineering, Volume 53, Pages 1187–1190.

I wasn’t expecting to find material for this blog on Mackinac Island, but I did. In 1822, Alexis St. Martin was accidentally shot in the abdomen in a small trading post near Fort Mackinac. Dr. William Beaumont was summoned to treat St. Martin, and was able to save his life. However, the wound healed in an odd way, leaving an opening providing access to the inside of his stomach.

Readers of the 4th edition of Intermediate Physics for Medicine and Biology will appreciate what happened next. The resourceful Beaumont took advantage of the situation to conduct experiments on digestion. He tied different foods to a string, threaded them into St. Martin’s stomach, left them to digest for a while, and then pulled them out to see what had happened. These ground-breaking experiments were instrumental in establishing how digestion works. I toured a small museum dedicated to Beaumont, which describes these experiments in graphic (perhaps too graphic) detail.

I am interested in Beaumont not just because of his experiments studying digestion. Beaumont Hospital, in Royal Oak Michigan, is the clinical partner for a new medical school recently established at Oakland University. The first class of students at the Oakland University William Beaumont School of Medicine arrives this August. This will be a landmark event in OU’s history, and we are all excited about it.

I can’t help but be intrigued by the juxtaposition of these two stories: William Beaumont’s experiments on Alexis St. Martin, and the establishment of a new medical school bearing Beaumont’s name. St. Martin lived into his 80s. I expect our new medical school will have a similarly long and productive life.

Opus 200

In August 2007 I began posting entries to this blog, in order to highlight topics discussed in the 4th edition of Intermediate Physics for Medicine and Biology. Since then, I’ve posted an entry every Friday morning, without fail. This is my 200th (excluding two rare non-Friday posts).

Why do I keep this blog? First, I hope it sells books. Second, I want a way to keep the book up-to-date. Third, some topics Russ and I only mention in passing, and this blog lets me explore these issues in more detail. Fourth, in the blog I often feature past scientists who contributed to the intersection between physics and biology. Fifth and finally, I enjoy it. I like writing, and I find the topics fascinating.

I get some help. Russ Hobbie often sends me ideas and suggestions. My daughter Kathy posted some key entries when I was in Paris and had very limited computer access. I particularly like comments (thanks Debbie). Feel free to voice your opinion. (However, I’m glad the bozo who posted links to porno sites in the comments has stopped.) I hope the readers find this blog useful.

Remember, the book website contains many useful items, including an errata (listing all known errors in the book), a reprint of our 2009 Resource Letter that appeared in the American Journal of Physics, a link to an interview with Russ Hobbie that appeared in the December 2006 Newsletter of the Division of Biological Physics, which is part of the American Physical Society, and (my personal favorite) a link to Russ Hobbie’s MacDose video on YouTube.

Finally, if you use Facebook, you can join the group “Intermediate Physics for Medicine and Biology” and receive these postings about the book there.

National Academies Press

Getting correct and detailed information about the applications of physics to biology and medicine is important. The 4th edition of Intermediate Physics for Medicine and Biology is an excellent source of such information. Yet I know that you, dear reader, are probably saying: “Yes, but I want a FREE source of information.” Well, for those cheapskates like me, there’s some good news this week from the National Academies Press (forwarded to me via Russ Hobbie). First, what is the National Academies Press? Their website explains:

The National Academies Press (NAP) was created by the National Academies to publish the reports issued by the National Academy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National Research Council, all operating under a charter granted by the Congress of the United States. The NAP publishes more than 200 books a year on a wide range of topics in science, engineering, and health, capturing the most authoritative views on important issues in science and health policy. The institutions represented by the NAP are unique in that they attract the nation’s leading experts in every field to serve on their award-wining panels and committees. The nation turns to the work of NAP for definitive information on everything from space science to animal nutrition.

Now, what’s the good news? An email from the NAP states

As of June 2, 2011, all PDF versions of books published by the National Academies Press (NAP) will be downloadable free of charge to anyone. This includes our current catalog of more than 4,000 books plus future reports published by NAP.

Free access to our online content supports the mission of NAP—publisher for the National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council—to improve government decision making and public policy, increase public education and understanding, and promote the acquisition and dissemination of knowledge in matters involving science, engineering, technology, and health. In 1994, we began offering free content online. Before today’s announcement, all PDFs were free to download in developing countries, and 65 percent of them were available for free to any user.

Like no other organization, the National Academies can enlist the nation’s foremost scientists, engineers, health professionals, and other experts to address the scientific and technical aspects of society’s most pressing problems through the authoritative and independent reports published by NAP. We invite you to sign up for MyNAP —a new way for us to deliver free downloads of this content to loyal subscribers like you, to offer you customized communications, and to reward you with exclusive offers and discounts on our printed books.

Intermediate Physics for Medicine and Biology cites several NAP reports. For instance, in Section 9.10 about the possible effects of weak external electric and magnetic fields, Russ and I cite and quote from the NAP report Possible Health Effects of Exposure to Residential Electric and Magnetic Fields. I tested the website (free just seemed too good to be true), and was able to download a pdf version of the document with no charge (although I did have to give them my email address when I logged in). I got 379 pages of expert analysis about the biological effects of powerline fields. Russ and I quote the bottom line of this report in our book:

There is no convincing evidence that exposure to 60-Hz electric and magnetic fields causes cancer in animals... There is no evidence of any adverse effects on reproduction or development in animals, particularly mammals, from exposure to power-frequency 50- or 60-Hz electric or magnetic fields.

In Chapter 16 on the medical use of X rays, we cite three of the Biological Effects of Ionizing Radiation (BEIR) reports: V, VI, and VII. These reports provide important background about the linear nonthreshold model of radiation exposure. Then in Chapter 17 on nuclear physics and nuclear medicine we cite BEIR reports IV and VI when discussing radiation exposure caused by radon gas. The full citations listed in our book are:

"BEIR IV (1988) Committee on the Biological Effects of Ionizing Radiations. Health Risks of Radon and Other Internally Deposited Alpha-Emitters. Washington, D.C., National Academy Press.

BEIR Report V (1990) Committee on the Biological Effects of Ionizing Radiation. Health Effects of Exposure to Low Levels of Ionizing Radiation. Washington, DC, National Academy Press.

BEIR VI (1999) Committee on Health Risks of Exposure to Radon. Health Effects of Exposure to Radon. Washington, D.C., National Academy Press.

BEIR Report VII (2005) Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation. Health Risks from Exposure to Low Levels of Ionizing Radiation. Washington, DC, National Academy Press.

Besides the reports cited in our book, there are many others you might like to read. In a previous blog entry, I discussed the report BIO2010: Transforming Undergraduate Education for Future Research Biologists, published by NAP. You can download a copy free. It discusses how we should teach physics to future life scientists. In another blog entry I discussed the book In the Beat of a Heart, which explores biological scaling. It is also published by the NAP.

Yet another report, published just last year, that will be of interest to readers of Intermediate Physics for Medicine and Biology is the NAP report Research at the Intersection of the Physical and Life Sciences. The report summary explains the goals of the report.

Today, while it still is convenient to classify most research in the natural sciences as either biological or physical, more and more scientists are quite deliberately and consciously addressing problems lying at the intersection of these traditional areas. This report focuses on their efforts. As directed by the charges in the statement of task (see Appendix A), the goals of the committee in preparing this report are several fold. The first goal is to provide a conceptual framework for assessing work in this area—that is, a sense of coherence for those not engaged in this research about the big objectives of the field and why it is worthy of attention from fellow scientists and programmatic focus by funding agencies. The second goal is to assess current work using that framework and to point out some of the more promising opportunities for future efforts, such as research that could significantly benefit society. The third and final goal of the report is to set out strategies for realizing those benefits—ways to enable and enhance collaboration so that the United States can take full advantage of the opportunities at this intersection.

An older report that covers much of the material that is in the last half of Intermediate Physics for Medicine and Biology is Mathematics and Physics of Emerging Biomedical Imaging (1996). Finally, yet another useful report is Advancing Nuclear Medicine Through Innovation (2007).

All this and more is now available at no cost. Who says there’s no such thing as a free lunch?

Jean Perrin and Avogadro’s Number

Regular readers of this blog may recall that last summer I visited Paris for my 25th wedding anniversary, which was followed by a string of blog entries about famous French scientists. During this trip, my wife and I toured the Pantheon, where we saw the burial site of French scientist Jean Baptiste Perrin (1870–1942). Russ Hobbie and I mention Perrin in a footnote on page 85 of the 4th edition of Intermediate Physics for Medicine and Biology.

The Boltzmann factor provided Jean Perrin with the first means to determine Avogadro’s number [N_A]. The density of particles in the atmosphere is proportional to exp(−mgy/k_BT), where mgy is the gravitational potential energy of the particles. Using particles for which m was known, Perrin was able to determine [Boltzmann’s constant] k_B for the first time. Since the gas constant R was already known, Avogadro’s number was determined from the relationship R = N_Ak_B.

This brief footnote does not do justice to Perrin’s extensive accomplishments. He played a key role in establishing that matter is not a continuum, but rather is made out of atoms. He performed experiments not only on the exponential distribution of particles (described above, and also known as sedimentation equilibrium), but also on Brownian motion. Russ and I describe this phenomenon in Chapter 4:

This movement of microscopic-sized particles, resulting from bombardment by much smaller invisible atoms, was first observed by English botanist Robert Brown in 1827 and is called Brownian motion.

Molecular Reality:
A Perspective on the
Scientific Work of Jean Perrin,
by Mary Jo Nye.

One can learn more about Perrin in the book Molecular Reality: A Perspective on the Scientific Work of Jean Perrin, by Mary Jo Nye. I would not rank this book with the best histories of science I have read (my top three would be The Making of the Atomic Bomb, The Eighth Day of Creation, and The Maxwellians), or among the best scientific biographies (such as Subtle is the Lord: The Science and Life of Albert Einstein). However, it did provide some valuable insight into Perrin’s achievements. Ney states in her introduction that

What has struck me in a perusal of the literature on these topics [discoveries in physics during the early 20th century] is the tendency to assume what so many of the physical scientists of this pivotal period did not for one minute assume—the discontinuity of the matter which underlies visible reality. In looking back upon the discoveries and theories of particles, one perhaps fails to realize that the focus was not simply upon the nature of the molecules, ions and atoms, but upon the very fact of their existence…

In analyzing the role of Jean Perrin in the eventual acceptance of this assumption among the outspoken majority of the scientific community, I have concentrated upon the period of experimental, theoretical, philosophical and popular science which climaxed with the Solvay conference of 1911 and with the publication of Perrin’s book Les Atomes [read an online English translation here] in 1913…

In conclusion, I have discussed the reception of Perrin’s scientific experimentation and propagandisation on the subject of molecular reality, especially his work on Brownian movement, which climaxed in 1913 with the completion of a number of national and international conferences and the publication of Les Atomes. Though Perrin himself did not view his task as completed at that time, the question was no longer central to the basic working assumptions of scientists, and polemics on this question were no longer an impediment or impetus to the progress of general scientific conceptualization. That Perrin’s role was historically essential to this denouement cannot, in my opinion, be doubted.

Nye’s first chapter on 19th-century background contains a little too much philosophy of science for my taste. But her historical review does indicate that, despite what our footnote says, Perrin did not provide the first estimate for Avogadro’s number, but rather provided a definitive early measurement of that value. Her second chapter about Young Perrin: Initial Investigations was better, and the book really captured my attention in the third chapter on The Essential Debate.

The exponential law which Perrin announced in 1908, describing the vertical distribution of a colloid at equilibrium, was the fruit of laborious experiments on Brownian movement after several years of apprenticeship in the study of colloids. Included in his first 1908 paper on Brownian movement was a successful application of the concepts of osmotic pressure and mean kinetic energy to the visible Brownian particles, as well as a convincing calculation of Avogadro’s number. These endevours were but the prelude to a five-year drama devoted to the erection of an unassailable edifice to house the dictum of molecular reality, a structure buttressed at its most vulnerable point of criticism by the observed laws of visible Brownian movement.

I was particularly fascinated by how Perrin knew the mass of the particles he studied.

In order to find m, Perrin utilized Stoke’s law [see Section 4.5 of Intermediate Physics for Medicine and Biology], applying it to a column of the emulsion in a vertical capillary tube, and observing the fact that when the emulsion is very far from equilibrium, the Brownian granules in the upper layers of the column fall as if they were droplets of a cloud. Using Stokes’ formula relating the velocity of a spherical droplet, its radius, and the viscosity of the medium, Perrin found the radius of the granules [on the order of a micron].

Then from the known density, he could determine the mass. Perrin had to go to great lengths to obtain particles with a uniform distribution of radii, starting with 1200 grams of particles and, after repeated centrifugation, ending with less than a gram of uniform particles.

In 1926, Jean Perrin won the 1926 Nobel Prize in physics “for his work on the discontinuous structure of matter, and especially for his discovery of sedimentation equilibrium.”