During the digestive processes the starchy, saccharine, and albuminoid elements of food are dissolved, and the fatty matters are emulsified. A uniform milky solution is thus formed, which is rapidly absorbed into the general circulation; some of it passes directly through the walls of the vessels into the blood, and some is taken up by the lacteals and reaches the vital fluid by traversing the complicated series of tubes known as the absorbent system, and the numerous glands connected with it. The chief function of the starchy and fatty food elements is to keep up the physical temperature, by being submitted to oxidation in the organism; therefore it is not necessary that they should experience any vitalizing change, but are fitted to discharge their duties in the vital domain by simply undergoing the solution that fits them for absorption. But the materials intended to enter into the composition of the body must be developed into living blood, in order to be fitted to become part and parcel of the organs by which power is evolved, and through the use of which we see, hear, feel, think, and move. This wonderful process begins and is carried forward in the absorbent system, which has been described by Dr. Carpenter as a great blood-making gland.

But the vital transformation is not completed until the nutritive materials have been submitted to the action of the liver, and afterward to the influence of oxygen in the capillaries of the lungs. The food that was eaten a few hours before is thus converted into rich scarlet arterial blood, if every part of the complex vitalizing processes has been properly conducted. But the influence of oxygen is requisite, not only to complete the vitalization of the embryo blood in the lungs, it is an absolutely essential element in every step of the vitalizing process in the absorbents.

The average quantity of food required to sustain an ordinary man in health and strength, I have previously stated, is about two pounds avoirdupois daily, and an equal weight of oxygen is necessary to the integrity of the vitalizing processes undergone by the food, and to maintain the physical temperature. When the requisite supply of oxygen is reduced, the extrication of heat within the system is promptly diminished, but the vitalization of digested food is unfavorably affected much more slowly, but with equal certainty. If the quota of oxygen existing in the arterial blood of the vessels whose duty it is to supply the vital fluid to the absorbent system, be inadequate to enable these operations to go on properly, the life-giving processes must necessarily be imperfectly accomplished. Under these circumstances the digested material is imperfectly vitalized, and is therefore inadequately fitted to be used in building up and repairing the living body. But its course in the system cannot be delayed, much less stopped.

The blood possesses a definite constitution, which cannot be materially altered without the rapid development of grave, perhaps fatal consequences. The nutritive matters received into the blood must be given up by it to the tissues for their repair, whether such materials are well or ill fitted for the vital purposes. Dr. B.W. Carpenter, of London, the celebrated physiologist, makes the following pertinent statements on this subject, which I condense from his great work on physiology: "We frequently find an imperfectly organizable product, known by the designation of tubercular matter, taking the place of the normal elements of tissue, both in the ordinary process of nutrition, and still more when inflammation is set up.

From the examination of the blood of tuberculous subjects it appears that, although the bulk of the coagulum obtained by stirring or beating is usually greater than that of healthy blood, yet this coagulum is not composed or well elaborated fibriae, for it is soft and loose, and contains an unusually large number of colorless blood corpuscles, while the red corpuscles form an abnormally small proportion of it. We can understand, therefore, that such a constant deficiency in capacity for organization must unfavorably affect the ordinary nutritive processes; and that there will be a liability to the deposit of imperfectly vitalized matter, instead of the normal elements of tissue, even without any inflammation. Such appears to be the history of the formation of tubercles in the lungs and other organs.

When it occurs as a kind of metamorphosis of the ordinary nutritive processes and in this manner, it may proceed insidiously for a long period, so that a large part of the tissue of the lungs shall be replaced by tubercular deposit without any other sign than an increasing difficulty of respiration." These views are strongly corroborated by the following facts:

In making post mortem examinations of persons who have died of consumption, tubercles of different kinds are found in the same subject; some of these, having been deposited during what is called the first stage of the disease before the breathing powers were much impaired, bear evident traces of organization in the form of cells and fibers more or less obvious, these being sometimes almost as perfectly formed as living matter, at least on the superficial part of the deposit, which is in immediate contact with the living structures around.

This variety of tubercle has a tendency to contract and remain in the lungs without doing much injury. But as the disease progressed, and the breathing capacity progressively diminished, tubercular matter occurs, evincing less and less organization, showing a tendency to break down and cause inflammation in the surrounding lung tissue, until at last we find crude yellow tubercles that have become softened, and formed cavities almost as soon as they were deposited.

Some cases of chronic consumption pass in a few months through the various stages from the deposit of the first tubercle to a fatal termination.

The progress of the disease is determined largely by the nature of the tubercular matter at the time it is deposited.

The variety of matter which has been partially vitalized commonly exists in small quantity, has a strong tendency to maintain its semi-organized condition unchanged by time, and rarely causes inflammation.

A small or moderate quantity of this sort of tubercle exists in the lungs of many persons, in whom it produces no tangible symptoms, and who are therefore quite unconscious of its presence; and even when it does exist in sufficient quantity to develop the symptoms of lung disorder, the progress of the disease is slow, often continuing for many years. It constitutes a variety of consumption which is specially amenable to proper treatment. On the other hand, the soft, yellow, cheesy, tubercular matter, which is totally destitute of any vitality, is too often deposited in large quantities, acts on the adjacent lung tissue as an active irritant, causes inflammation, undergoes softening, forms cavities, defies treatment, and rapidly hurries the sufferers to a premature grave. These facts, taken in connection with the immunity from lung diseases enjoyed by those whose respiratory capacity is well developed and properly used, as well as the beneficial effects that are promptly secured in the favorable varieties of consumption by any important increase in the vital volume, I believe fully justify the statement that tubercles are the results of defective nutrition directly traceable to inadequate respiratory capacity, either congenital or acquired - in other words, tubercles are composed of particles of food which have failed to acquire sufficient life while undergoing the vital processes, because the person in whom they occur habitually breathed too little fresh air.

Persons who possess what is called the scrofulous constitution are specially liable to the occurrence of tubercular matter when their respiration is defective, or they are exposed to any other influences that favor its development in the organism. But habitually defective respiration, or the breathing of an atmosphere containing too little oxygen, which practically amounts to the same thing, has a very powerful tendency in the same direction, in persons who are apparently as free from scrofulous taint as any human being can be.