This theory is probably older than the one we have just mentioned, but as a causation of chronic disease intestinal autointoxication has only come to the front in recent years. To my mind it is certainly a much more feasible explanation of the origin of disease than any other yet advanced, because we are yet so slightly acquainted with the intimate processes at work in the living tissues, that we are unable to appreciate it at its full significance.

Briefly the proposition consists in the statement that the undigested portions of our food become a prey to microbes in the intestinal canal, and that highly toxic or poisonous substances are thus formed which are absorbed into the blood, and so act deleteriously on the body. The alimentary canal, we know, is haunted by countless numbers of germs, and it has been computed that at least 128,000,000,000,000 are discharged each day in the faeces. Fortunately for us they are divided into two classes: (1) Those which live on the remnants of protein food, the toxins of which are most deadly in character; (2) Those which prefer fats and starches, the by-products of which are much less irritating to the body. These rival sets of microbes are continually at war with each other, and the harmless set have no compunction in annihilating their more lethal opponents.

If therefore one provides a sufficient amount of pabulum in the shape of starchy or sugary food, we may expect an excess of these harmless inhabitants of our intestine and a corresponding diminution of those liable to occasion trouble. This is the conception underlying the "curdled" milk treatment, because not only is a large quantity of sugary matter provided in the milk, but the germs themselves are supplied in abundance in the hope that they may establish themselves in the colon and so overcome its dangerous denizens.

On the plea that flesh foods always provide a large surplus of indigestible material from which the microbes of putrefaction may produce toxic substances, one section of the vegetarians not only eschews fish, flesh, and fowl, but also limits the quantity of vegetable protein to very small proportions. It is also claimed that vegetable protein is much less putrefiable than the animal variety, but this is more or less conjectural, and in any case, largely because of its surrounding envelope of cellulose, a greater proportion of it is undigested and unabsorbed than of animal protein.

It may be laid down as a general principle that where-ever you provide a supply of food for them, colonies of microbes will establish themselves and flourish in accordance with the quantity and nature of their nutriment. Now there is always a residue of proteins, fats, and carbohydrates in the colon, and we must therefore expect to find different varieties of micro-organisms in the lower bowel, but it is by no means a foregone conclusion that their by-products will produce a malign influence on the body. In any case it is unfair to lay the blame of any such deleterious effect on the by-products of the proteins alone without reference to those of the fats and carbohydrates, for the latter produce many irritating acids which are capable of absorption, and so of becoming problematical factors in the causation of disease in the body.

Doubtless ere this many of my readers are inquiring why, if the facts be as I have stated, every individual is not suffering from disease in some form, and his query is perfectly apt and pertinent. It is to be hoped that the reply will be satisfactory and illuminating. The truth is that Dame Nature recognised this very difficulty from the beginning and laid her plans to obviate it. In the first place, the various digestive fluids, and in particular the hydrochloric acid of the gastric juice, are decidedly antisceptic, and consequently antimicrobic, while the lining membrane of the whole alimentary canal not only excretes a healthy mucus which acts as an antidote to the toxins of the micro-organisms, but the living wall itself, so long as it is intact, is an effectual barrier to their access into the blood. Finally, in normal circumstances, and certainly in the healthy individual living and working in the open air, the bowels empty themselves of their poisonous contents frequently and at regular intervals. Where this does not take place there is more chance of absorption, although, strange to say, in fairly severe constipation, probably because of the lack of moisture in the colon, the effects are often apparently less serious than where there is simply an insufficient daily evacuation.

Even when the toxins have been freely absorbed, Nature is not forgetful of her protective functions, for she has in the first place planted the fiver with its internal purifying arrangements as a huge destructor to nullify the poisonous emanations of the colon, and the most feasible explanation of "biliousness" is that the fiver resents an overplus of work in this direction and violently proclaims her objection. But the upheaval is more than a protest, for it is likewise an effective means of ridding the system of superfluous and probably dangerous material. When for any reason the fiver becomes complacent enough to cease its rejection of such material, almost invariably other and more serious conditions arise. For the poison now obtains access to the blood and sets up headache, skin diseases, rheumatism, asthma, or some such malady, although there are special means provided for metabolising the toxins in the thyroid and other ductless glands.

When they are unable to be metabolised then, an effort is made to excrete them by the skin, the kidneys, and the lungs, and no doubt many diseases of those organs arise in this manner. The doctrine of intestinal auto-intoxication is thus a fascinating one, and provides an explanation of the onset of disease which is at once simple and satisfying. Needless to say it is not the whole explanation, but it is full of promise of good health for the man who acts upon it by keeping his bowels open, his skin active, and his lungs free and easy by exercise in the open air.