It was not easy to study the process of digestion. It was as late as the turn of the last century that the Russian scientist Ivan Petrovich Pavlov completed a detailed study of the main alimentary glands. They turned out to be numerous and, what is more, it was discovered that for each type of food they produce a special composition of digestive juices. Academician Pavlov was awarded the Nobel prize, the highest international award, for these investigations. Thus, the basic mystery surrounding the process of digestion seemed to have been unveiled. However, the discovery was not yet complete. Nobody could reproduce the entire process of digestion in the laboratory by pouring into a test tube the necessary digestive juices in the correct sequence, and thus imitating the process observed in living organisms under natural conditions. The food was also digested in the test tube, but the process was all too slow, much slower than in the alimentary tract.

Recently, scientists have succeeded in uncovering this mystery. An astonishing thing is that the food which comes into contact with the intestinal wall is digested much more quickly than that incorporated in the main mass of food. This is similar to what happens when food is fried in a pan: the food in immediate contact with the walls of the pan cooks much more quickly. This is quite under­standable, for the pan is much hotter than the food. But the intestinal wall is not at all hot, so why then does it accelerate digestion?

The first thing was to find out whether the intestinal wall ready accelerated digestion. With this in view, the following experiment was carried out. A piece of intestine from a freshly killed animal was placed in one of two test tubes containing equal amounts of a mixture of starch and an amylase (a starch-splitting enzyme). Splitting of the starch proceeded much more rapidly around the piece of intestine which proved that the intestinal wall did accelerate digestion. But how does this happen?

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