In the early 20th century, Carl von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying <answer>principles of physics</answer> in nutrition. In 1906, Edith G. Willcock and Frederick Hopkins showed that the amino acid tryptophan aids the well-being of mice but it did not assure their growth. In the middle of twelve years of attempts to isolate them, Hopkins said in a 1906 lecture that "unsuspected dietetic factors," other than calories, protein, and minerals, are needed to prevent deficiency diseases. In 1907, Stephen M. Babcock and Edwin B. Hart conducted the single-grain experiment, which took nearly four years to complete.
What did Carl von Voit and Max Rubner apply to nutrition in order to receive their results?
principles of physics