There are, however, a few of these "oversights" which are of little or no known utility, and yet which, either by their structure or situation, may become the starting-point of serious trouble. The best known members of this small group are the openings through the abdominal wall, which, originally placed at the strongest and safest position in the quadrupedal attitude, are now, in the erect attitude, at the weakest and most dangerous, and furnish opportunity for those serious and sometimes fatal escapes of portions of the intestines which we call hernia; the tonsils; and our friend the _appendix vermiformis_. For once its name expresses it exactly. It _is_ an "appendix," an afterthought; and it is "_vermiformis_," a worm-like creature,--and, like the worm, will sometimes turn when trodden on. Its worm-likeness is significant in another sense also, in that it is this very diminutiveness in size--the coils into which it is thrown, the spongy thickness of its walls, and the readiness with which its calibre or its circulation is blocked--that is the fundamental cause of its tendency to disease. The cause of appendicitis is the appendix. "Despise not the day of small things" is good pathology as well as Scripture. Here we have a little, worm-shaped tag, or side branch, of the food-tube, barely three or four inches long, of about the diameter of a small quill and of a calibre that will barely admit an ordinary knitting needle. And yet we speak of it with bated breath. When we remember that this little, twisted, blind tube opens directly out of one of the largest pouches of the intestines (the _caecum_), and that it is easy for anything that may be present in the large pouch--food, irritating fragments of waste matter, or bacteria--to find its way into this fatal little trap, but very difficult to find the way out again, we can form some idea of what a literal death-trap it may become. How did such a useless and dangerous structure ever come to develop in a body in which for the most part there is mutual helpfulness, utility, and perfect smoothness of working through all the great machine? To attempt to answer this would carry us very far back into ancient history. But to make such backward search is absolutely the only means of reaching an answer. "But," some one will object, "how perfectly irrational, not to say absurd, to propose to go back hundreds of thousands of years into ancient history, to account for a disease which has been discovered--according to some, invented--within the past twenty-five years!"