First printed in 1983, this book concerns the comparative physiological adaptations of vertebrate animals, especially mammals, to cessation of breathing. These adaptations were originally identified in species living in aquatic habitats. The argument is presented that the natural divers display a well-developed and conveniently studied example of a more general defence against asphyxia. The topics considered include the diving response, metabolic and cardiovascular adaptations, variations in resistance to asphyxia, neural control mechanisms, which govern the respiratory and circulatory responses, perinatal asphyxia, applications to the human species and medical implications. The book's purpose is to acquaint its readers with some advances resulting from research in this field.