74 books • 10 series
Book #1: The Astounding Nervous System: How Does My Brain Work?
Book #2: The Dynamic Digestive System: How Does My Stomach Work?
Book #3: The Remarkable Respiratory System: How Do My Lungs Work?
Book #4: The Amazing Circulatory System: How Does My Heart Work?
Book #5: The Exciting Endocrine System: How Do My Glands Work?