This advertisement from Singapore in the early 1930s more or less says the following:

“When going for a drive, your energy and mental capacity must be at their fullest in order to avoid an accident, and to feel happy. A person’s body is like an engine. It needs enhancing products to support and nourish it. Only then can it become strong and lively. If not, it will become daily weaker and one will not be able to work. Ovaltine is a nourishing and delicious drink, which possess the great ability to brink back strength and increase vigor. Drinking it after a day of work and toil, and it will immediately reveal its amazing efficacy. Buy some and give it a try!”

A couple of months ago I posted an advertisement from Thailand for Sinkesin – the “famous medicine for preserving sex glands in their normal state.” That advertisement had a line which read, “The complexity of the body is like the complexity of an engine.”

This leads me to suspect that comparing the body to an engine is probably a concept which became popular during this period as the world entered the automotive age. That’s a good topic for some enterprising graduate student to research.