Which C.S. Lewis book introduced the phrase “men without chests” in its title chapter?

The C.S. Lewis book that introduced “men without chests” is The Abolition of Man.

The Abolition of Man began as a series of three lectures delivered at the University of Durham in 1943. Lewis published them as a book in 1943, with the chapters titled “Men Without Chests,” “The Way,” and “The Abolition of Man.” He argued against an approach to education that treated value judgments as nothing more than subjective emotional responses.

In Lewis’s argument, the “chest” symbolically represents the trained affections: the part of a person that connects reason with emotion and moral action. The phrase is sometimes misunderstood as a literal reference to anatomy or physical courage. It is instead part of Lewis’s philosophical criticism of moral relativism and educational theory. The book also discusses what Lewis called the Tao, a term for a cross-cultural body of basic moral principles.