Kind of a weird product, but a reasonable primer on a handful of physiology topics. It assumes a very specific level of prior knowledge which may have been reasonable among zoology undergrads 50 years ago, but just seems poorly explained now. As well, Schmidt-Nielsen's writing isn't always as clear as it could be. The figures are a mixed bag; many of the drawings are difficult to interpret, but the graphs at least are straightforward. It's a shame, because it's worth learning about stuff like how birds breathe and the difference between a counter-current exchanger and a counter-current multiplier. You just kind of already have to know a fair bit about these things in the first place to enjoy this book.