Recently I heard somewhere about this classic,”The fire of Life,” by a famous scientist and teacher, Max Kleiber, subtitled “an introduction to animal energetics.” But it was hard to get a copy. It’s out of print, and even though it went through five editions, it seems to have become scarce on the used book market. The used book sellers through Amazon wanted $200 and $900 for one. It’s not findable online as a PDF. I finally got a copy through Shawnee State University library by interlibrary loan, but that took awhile.
Despite it’s romantic title, it’s not light reading. It turned out to be a heavy college textbook. It’s lots of physics and chemistry and physical chemistry and math. First published in 1961, my copy was a 1975 second edition. Maybe because it is old, I can mostly almost understand the math. He even provides valuable math lessons in multiple appendices. In the preface to this edition, Professor Kleiber says that “the most decisive discoveries in the field of animal energetics are over a century old.” So it’s still not out-of-date information. But when he wrote this book, there was a movement afoot to get rid of calories and use joules in nutrition science. So you know how that turned out. A calorie is the amount of heat needed to raise 1 gram of water 1 degree centigrade. A joule is the amount of energy needed to pick a 100 gram weight up 1 meter. All forms of energy are interconvertable, and 1 calorie equals 4.18 joules. The joule is named after James Prescott Joule, an English physicist who built a machine that demonstrated that a weight on a string turning a propeller to churn a certain amount of water raised the temperature of the water, thereby demonstrating that interconvertability of different forms of energy. p110
Reading the chapter headings, this would appear to be a book about starvation. But first it is necesary to understand metabolism of the energy in food.
It all started with Joseph Priestly, who came to America in search of religious freedom in 1761. That was before Donald Trump. He made the following observations: After a candle goes out in a closed bottle, the air in there makes it impossible to relight a candle. After a mouse dies in a closed bottle, you can’t light a candle in there. A mouse and a lit candle both die at the same time in a closed bottle. At first he thought they were putting something into the air he called phlogiston. But then after more spiffy experiments, he and Lavoisier in France and others figured out they were using something up instead of adding something fatal to fire and discovered oxygen, a name coined by Lavoisier that means “acid former.” Thus, “the fire of life” — metabolism is a controlled fire.
Many olden day experiments that were not free of harm to animals have shown that the metabolism of small animals is faster than that of big animals. The “surface law” also known as Rubner’s rule says that an animal’s metabolism is roughly proportional to that animal’s surface area. The metabolic rate in calories per day is 1,000 times the body surface area in meters squared. Except for rabbits, which have big ears with a lot of surface area that screws up the rule. Little animals have more surface area per pound of body weight. The surface area of an animal is proportional to the 2/3 power of their weight. The 2/3 power means square the weight and take the cube root of that. The cube root of a number is smaller than the square of a number is bigger. So as an animal gets bigger, his surface area and basal metabolism gets smaller per pound. A pound of elephant has a smaller amount of surface area and metabolic rate that a pound of mouse. It turns out that the metabolic rate of animals is even more tightly proportional to the 3/4 power of their weight. Why is that? Well, read chapter 10. Oh, yeah, you probly can’t find chapter 10. Anyway, it’s complicated and contentious.
Further gems from “The fire of life”
— A dead turtle cools off more slowly than a live turtle.
— A rat starves to death faster when kept in a colder environment than in a warmer one, but only up to 86 degrees Fahrenheit, then he starves faster as you raise the temperature further.
— The old word for concentrated sulfuric acid is oleum, which means oil in Latin, so don’t get confused and think that a bottle labeled “oleum” it’s just oil and cause a disaster.
— Even with unlimited food supply, animals periodically stop eating. The medical doctor seeks to allow the enjoyment of a high food intake with a minimum of fattening, but the farmer seeks methods of maximum fattening with minimum food.
It’s not all hard data. There’s history and anecdotes and philosophy.
So there you have it, “The fire of life” in a nutshell. But that’s like saying there you have Chinese in a nutshell. Max Kleiber’s classic is an encyclopedia of basic science, and it should be on the reference shelf of every fat scientist. But I am going to have to return it to the library.
1. Davis WJ et al. Long‐Term Weight Gain and Risk of Overweight in Parous and Nulliparous Women. Obesity April 2018 https://doi.org/10.1002/oby.22174
John DiTraglia, M.D., is a pediatrician in Portsmouth. He can be reached by email at firstname.lastname@example.org or call 740-354-6605.
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