It's what keeps the hospital functioning, so we can treat everyone who comes this way.
Regarding disorders and disabilities: We should be able to repair, heal, or replace any part of the body not functioning at the level the person with the disability reasonably wishes it to.
In a few cases some of the tracheids have very thick walls and reduced cavities, functioning as mechanical rather than as waterconducting elements.
The embryo passes through three stages - (I) still enclosed within the egg and living on its own yolk; (2) free, within the vitelline mass, which is directly swallowed by the mouth; (3) there is no more vitelline mass, but the embryo is possessed of long external gills, which serve for an exchange of nutritive fluid through the maternal uterus, these gills functioning in the same way as the chorionic villi of the mammalian egg.
The whole functioning of our mental apparatus is directed upon yielding the right response to the stimulations of the environment, and is valuable if and in so far as it does this.