If you do farming work, your brain becomes hardened for farming;
if you study, your brain becomes hardened for studying;
and if you sleep a lot, your brain also becomes hardened for sleeping a lot.
The brain is also [part of] the physical body.
Just as the body develops certain constitution,
the brain develops certain constitution also.
If it becomes the constitution,
the color of the brain changes just like a green leaf changes its color [in autumn.]
