Textbooks are comparable to living organisms. Although some come into the world stillborn, or with negligible vitality, others grow lustily. They get larger and larger, older, and more venerable. Then they may become subject to a form of cancer, of undisciplined proliferation of parts, until they no longer can survive in a changing environment and die off.
The pathogenesis of this malignant growth is directly traceable to specialization. In the early phases of most subjects—whether histology, public health, genetics, physical examination, cardiology, or what-not—the areas were sufficiently limited so that one man could encompass the entire field. Indeed, authors of early textbooks may have been among the pioneers. As knowledge accumulated, and as an author got older and could no longer keep up with all the latest developments, he called on others with more specialized knowledge to write specific chapters. This stimulus to multiplication of authors might go on unchecked.