We must now pass on to consider the method whereby these various alimentary principles are made available for the purposes of the body, and although the subject is one of entrancing interest, we must dismiss it in the briefest fashion compatible with its appropriate comprehension.

With the exception of water, none of the alimentary principles are in a state capable of incorporation with the body cells. Without being dissolved in some form or other they are unable to enter the circulation, and it is quite possible that even water undergoes some change before this occurs. To effect this change some process is therefore essential, and for this purpose the various organs of digestion exist. The shortest and most arresting definition of digestion indeed is solution, and in any case this is the keynote of the various changes produced by the digestive fluids.