as light, temperature, oxygen tension, and hormone balance, comparative physiology uses, in addition, species or animal type as a variable for each function." 25 years later, Prosser put things this way: "I like to think of it as that method in physiology which uses kind of organism as one experimental variable." Comparative physiologists often study organisms that live in "extreme" environments (e.g., deserts) because they expect to find especially clear examples of evolutionary adaptation. One example is the study of water balance in desert-inhabiting mammals, which have been found to exhibit kidney specializations. Similarly, comparative physiologists have been attracted to "unusual" organisms, such as very large or small ones. As an example, of the latter, hummingbirds have been studied. As another example, giraffe have been studied because of their long necks and the expectation that this would lead to specializations related to the regulation of blood pressure. More generally, ectothermic vertebrates have been studied to determine how blood acid-base balance and pH change as body temperature changes. Funding In the United States, research in comparative physiology is funded by both the National Institutes of Health and the National Science Foundation. Societies A number of scientific societies feature sections on comparative physiology, including: American Physiological Society Australian & New Zealand Society for Comparative Physiology & Biochemistry Canadian Society of Zoologists Japanese Society for Comparative Physiology and Biochemistry Society for Integrative and Comparative Biology Society for Experimental Biology Biographies Knut Schmidt-Nielsen (1915–2007) was a major figure in vertebrate comparative physiology, serving on the faculty at Duke University for many years and training a large number of students (obituary). He also authored several books, including an influential text, all known for their accessible writing style. Grover C. Stephens (1925–2003) was a well-known invertebrate comparative physiologist, serving on the faculty of the University of Minnesota until becoming the founding chairman of the Department of Organismic Biology at the University of California at Irvine in 1964. He was the mentor for numerous graduate students, many of whom have gone on to further build the field (obituary). He authored several books and in addition to being an accomplished biologist was also an accomplished pianist and philosopher. Some journals that publish articles in comparative animal physiology American Journal of Physiology - Regulatory, Integrative and Comparative Physiology Annual Review of Physiology Comparative Biochemistry and Physiology Integrative and Comparative Biology Journal of Comparative Physiology Journal of Experimental Biology Physiological