Of uneven quality. When Gibbons is telling crazy stories, he's hilarious and an all-around blast. When he's starts lecturing or preaching, he's something of a mildly benevolent bore. Still fun, and a good read-aloud if skimming isn't against your religion.
Their Blood Runs Cold is a mixture of basic information about the main groups of amphibians and reptiles (frogs, salamanders, turtles, snakes, and lizards) along with stories from the author who had a long and illustrious career as a herpetologist in the southeastern US. The books in now more than 40 years old, but most of the basic info still holds up. The best parts of the book are stories by Gibbons about various adventures working with amphibians and reptiles. And the best story in the book is about Gibbons and his assistant trying to catch an alligator and get it into the back of a pick-up.
Colorful and amusing accounts of field herpetology. Not a dull read by any means. I would recommend it to anyone, whether or not they think they have any interest in herpetology or biology.
Some interesting anecdotes, but also there is a lot of old out of date "just collect everything you find". Conservation has advanced extensively since this book was published.