Also in Vol. 5, Metaphysics, The Experience of the Soul Through the Different Planes of Existence, 1. Our Physical Constitution, The Elements of the Body

Our physical body is constituted of the five chief elements, which compose even the whole universe.

The skin, flesh, and bones show earth properties;
And the blood, perspiration, and saliva represent the water element.
The heat in the body and the digestive fire in the system denote the fire element.
The breath and its inner work within the body, which enable us to stretch and contract, and the power of movement, which does not allow us to keep still for one moment, represent the air element.
The ether element in us is that which controls our activities and gradually consumes All other elements. It is for this reason that a child is more active, while an aged person is still and inclined to inactivity.

The above is a rough explanation of the different parts of the body representing the different elements. They correspond in the following way:

the bones with the earth element;
the flesh with the water;
the blood with the fire;
the skin with the air;
the hair with the ether.

Bone is as void of sensation as the earth.
The shrinking and swelling of the muscles, the festering of the flesh, and the effect of water on it both inwardly and outwardly, prove that the flesh corresponds to the water element.
The circulation of the blood depends absolutely upon the degree of heat; it flows as the fire element makes it.
The air influences the skin. In hot weather the skin becomes darker, and in cold fairer; in rough weather it becomes rough, and in fine weather smooth. All different shades of the skin are mainly due to the climatic conditions of our place of birth and dwelling.
The hair corresponds with the ether and is the least sensitive. If the hair is cut or burned there is no sensation.

The outlet of each different kind of refuse is caused by a certain element.

The [bowel] motion is caused by earth,
urination by the water element,
perspiration by fire,
saliva by air,
semen by ether.