After a meal, or, rather, when the process of digestion is over and the animal is beginning to think about its next, the gland cells start preparing their enzyme. There is great activity in the nucleus, and granules stream out from it towards the lumen of the gland in much the same way, to take a homely illustration, as bubbles in some effervescing drink form at the bottom of the tumbler and rise till the surface is covered with foam. At the right moment these granules are discharged, just as the bubbles on the surface of a liquid break at a slight jog. They are usually not the ferment or enzyme, but its precursor, a substance which only turns into the ferment when it gets outside the cells. The ferments, when formed, are very peculiar substances about which we should like the chemist to tell us more, though great advances have been made in our knowledge of them lately. Among other peculiarities, one may mention that, though they will keep indefinitely if bottled, they are easily destroyed by too extreme a temperature or too acid or alkaline surroundings, that their composition is entirely unknown, and, strangest of all, that they do not become used up. A given amount of rennet will clot any amount of milk within reasonable limits, and yet remain rennet. The clergyman has been quoted as an illustration of the action of a ferment, and he makes a good one. He can make any number of suitable men and women into married couples, and yet his own state is unchanged. III. In man, the digestive process may be divided into three stages. They are arranged progressively, so that each clears the way for the next, and take place in the mouth, the stomach, and the upper part of the small intestine, the rest of the canal being mainly occupied in absorption. [Illustration: DIAGRAM 10.—GENERAL SCHEME OF THE ALIMENTARY CANAL, WITH ITS OFFSHOOTS—LUNGS AND GLANDS.] By far the largest proportion of the food is carbohydrate, in some form, so one naturally expects the first stage of digestion will deal with the constituents which represent this class. This is the case. The food is taken into the mouth in small quantities and ground up with the teeth, during which process it is subjected to the action of the saliva. This fluid, which is the secretion of three pairs of glands, converts a large proportion of the carbohydrates, starch, cane-sugar, etc., into a very simple sugar which is absorbed directly it reaches the stomach. One of the most sensational discoveries of the physiologist has been that the saliva leaving the gland does not contain the ferment necessary to effect this change until it has been subjected to the action of putrefactive bacteria. These, fortunately for us, it is pleasant to know, simply swarm in the mouth.