The Magic School Bus Inside the Human Body is the third book in the book series.
After Ms. Frizzle teaches her class about the human body, she shrinks them and the bus, except Arnold, who swallows them. This gives Cole and Degen a chance for two parallel stories, inside and outside of Arnold. With the bus inside, Cole explains digestion from the stomach into the small intestine. Then the bus enters a blood vessel where readers can see through the plasma where red and white blood cells fighting germs and they flow into the heart. From there the class, now out of the bus and garbed in operating room smocks and masks, flow with the red blood cells, now with fresh oxygen, to the brain. From there they climb down the bones of the spine, follow nerves to see muscles work, and then finally catch up with the bus to emerge into the nasal cavity. Meanwhile, Arnold has coped with being lost and alone and has made it back to the school. With one sudden sneeze, he sends the bus into out the parking lot where it returns to full size. The class can now chart the body from actual experience.
- Unlike in the episode "For Lunch", the students never realize that they are inside Arnold's body, however, Phoebe says that she feels as though he is close by.
- While the first half of the field trip in the book serves as basis of "For Lunch", the second half likely inspired both "Inside Ralphie" and "Works Out".
- This is the second book to not have the Bus transform into anything. The first time was At The Waterworks.
- In the republished version, the Bus had GURGLE! as its overhead sign.
- There is another version of the book where it’s like the original book cover, except ”The Magic School Bus” was in a different font & the title ”Inside The Human Body”, was in Times New Roman.
- On the back of the original book cover, Arnold is seen holding his stomach in sadness (Similar to Pg.13), with the robin sitting beside him, (Except in paperback version, the robin is blocked out by the rectangular box filled with names, credits and list of other Magic School Bus book titles).