We arrive then at the one great question:  What is the cause of disease? Not of one or other form of disease or class of diseases, but of disease as a whole.

There is, in fact, only one disease.

What appear to us as different disturbances of the normal condition of our body, are only variations, in quantity or in quality, of the one thing.  It is the variation of the controlling element which performs the necessary work of keeping the existing cells in proper condition and replacing those which in the course of nature are destroyed.  In a word, the work of perpetual regeneration, which is life.

METABOLISM.

This continuous changing of the entire human body,—­the removal of the discarded cells, burned up by oxidation and expelled from the body in the urine, the perspiration and other excretions, and their replacement by new ones,—­is called metabolism, that is, “change of matter.”

This change is brought about by means of a vital fluid in the body, which circulates from the moment in which the spermatozoon, or male seed, touches the female egg in the womb of the mother, until the time of our last breath.  That fluid is the blood,—­the carrier of nature’s supplies to all parts of the body for the rebuilding of cells; the exact and equitable distributor in quantities of material which determines the quality of the cells.

In its marvelous performance of this function, the blood is the bearer of the sole existing condition of health; namely the necessary elements of cell-building in the right proportions.

This is health, and the lack thereof is disease.

The demand of nature for upbuilding and rebuilding is the strongest instinctive impulse of our being; and this being so, a wrong proportion may cause the upbuilding of things which are different and disturbing to the normal organism.

But, on the other hand, kindly nature exhibits an ever existent inclination to counterbalance any disturbance in the right proportion, and to bring back conditions to uniformity.

We may thus justly speak of the overwhelming healing tendency of nature.

Metabolism is, therefore, the one great dominant function of the body which, accordingly, must have our especial care.

It is the blood, consequently, to which alone we can resort if we desire to assist nature in its process and tendency of balancing and healing.

This again indicates that, notwithstanding the apparent great variety of constitutional diseases, they are all practically one and the same disease.  They are all disturbances of proper metabolism, by some irregularity of the quantitative or qualitative condition of the blood.

This governing truth the great physiologist, Prof.  Jacob Moleschott, has formulated in the memorable words:  “It is one of the chief questions which humanity must always ask of the physician:  how to attain good, healthy and active blood.  And, view the question as we may, all who give it serious thought, are forced by experience to acknowledge explicitly, or otherwise, that our mental and physical capacity, and likewise the power of reproduction, are directly dependent upon our blood, and our blood on our nutrition.”