For so many years we have labored under the old habit of meat, bread and potatoes, calling them "plain foods," that it is not easy at once to look on this arrangement as harmful.

Yet it is violently acid-forming in character, as will be realized by referring again to the last chapter on The Mechanism of Digestion.

It is men who have lived on these "plain things" that in their later years develop diabetes or Bright's disease or other of the acid conditions that shorten the latter end of life needlessly, and not the wide eater of everything, who stands a better chance to have taken on more alkalin or base-forming foods by this more liberal manner of feeding himself.

This class of foods called carbohydrate includes all the starchy and sweet things of the table, so bread, being starchy, also potato, the stage is set for an alkalin digestion, for you will recall that we , told you in last chapter that these foods require alkalin conditions for their digestion throughout the entire tract, and that the introduction of acid at any point in this process will arrest this, with resulting fermentation.

You will further recall that the proteins require an acid treatment as the first step in their digestion in the stomach, and meat, being a concentrated protein, requires this acid bath, Nature providing this as the first necessary step in the digestion of this class of foods, to soften the fibrous capsule that surrounds the individual components of all organized protein.

Without this preliminary bath in hydrochloric acid the work of reduction to the primary forms of protein, the ultimate mono-proteid of the intestinal chyme, the work is so seriously handicapped that we recognize the almost impossibility of the digestion of meats by any one who does not show hydrochloric acid in the stomach after the ingestion of any concentrated protein, and we give such patient this acid as an aid to digestion.

Nearly thirty years ago Pawlow, the great Russian physiologist, then residing in Paris, took dogs of all sizes and conditions, and making a hole in the stomach, that was closed with a stopper, studied the effects of various foods on the condition and composition of the gastric juice, and he found that this contained no hydrochloric acid till after the entrance of meat or some other form of concentrated protein, that is, the gastric juice would form on sight or smell of food, and could be drawn off and examined, but till the meat actually entered the stomach there was no hydrochloric acid found in this, proving that this acts by its presence to stimulate the flow of the acid.

Dogs were allowed to eat meat freely, and the stopper was left in till digestion was well under way, and the percentage of hydrochloric continued to rise till the meat was well mixed with the gastric juice when no more was secreted till the next introduction of meat.

Now if this works out the same with the human, it is easy to see that when we eat meat and bread together we have set an alkalin task and immediately interrupted this by an acid task, an incompatibility in task that no human or other stomach could possibly overcome, for no stomach could be at the same time both acid and alkalin, just as no room could be at once both light and dark, the two being opposites, so that one or the other would prevail.

Acids may be so completely neutralized, or bound, by alkalies that there is an exact neutral point, when the medium is neither acid nor alkalin, as we show continually in the laboratory in making certain tests.

If the medium were neutral then neither starchy nor protein digestion could go on, as the one can occur in nothing less than a positive alkalinity, and the other in a positive acidity.

Hence, you see that this mixture of starches with concentrated protein is a clear incompatibility, making it impossible for one of. these dissimilar foods to digest, and if the medium is completely neutralized, neither acid nor alkalin, as by the presence of just enough alkalin saliva to neutralize completely or bind the amount of hydrochloric acid present, then neither of these foods would digest, fermentation would result, acids would form, and, in the case of the meat, an early putrefactive change would set in, as occurs so often in ptomaine poisoning.

This is perhaps the commonest incompatibility generally practiced in selecting and combining the foods, and is, no doubt, responsible for more acids than is any one mistake of the many that are made every day at almost every table in the whole land.

Now, if acid negatives the digestion of the carbohydrate foods, then we can see that the use concurrently of starchy or sweet foods with an acid fruit must act in the same way, for these fruit acids remain just long enough in the stomach to cause the arrest of the ptyalin ferment mixed with the food as it is chewed and insalivated in the mouth, and once arrested it cannot again resume, fermentation having already set in.

So not only must we avoid the mixture of meats with our starchy or sweet foods, but also the acids of fruits or any form of acid whatever.

When starchy digestion is arrested fermentation sets in at once, and fermentation produces acid; this is absorbed, and our alkalinity is reduced, and as alkalinity is reduced the acidity, of course, rises proportionately, for a reduction in alkalinity is exactly the same thing as a rise in acidity.

Every function of the body is carried on in an alkalin medium except the first step in the digestion of protein, which is an acid act, and occurs only in the stomach; and function is well proportioned to the degree of alkalinity, the higher this, within the normal limits, the more active and perfect will be function.

For this reason Nature provides us with a very considerable alkalin reserve on which we draw for the neutralization of acids, and when we lower this alkalin reserve we interfere with normal function to this degree.