It is logical that the thicker the appendix, the more pronounced will be the marks produced by the pressure of the psoas. The average size of the appendix, even in the adult, is that of a somewhat slender worm, from which is derived the name “vermiform appendix.” But when there is stagnation of the fæcal contents in the appendix, and especially when the thickened fæcal matters are of such hard consistency that a hard stony concrement, such as the coprolith is formed, then the appendix sometimes assumes quite a comparatively large size. We saw the case of a girl of 16, operated on by Dr. Offerhaus at the Hague (details of which case were published by him), in whom the appendix was of the size, in circumference, of a large thumb. In such large appendices the marks of the psoas will, of course, be more pronounced, and frequently the narrow bridge referred to will develop. This is caused by the appendix being further attached to the intestines where, owing to the narrow connecting bridge, it is unable to evacuate itself, and so grows larger and larger, the mischief thus constantly increasing. It is also evident that the nutrition of an organ whose blood-supply is mechanically interfered with, as in the case of the appendix by its close contact with the psoas, as described above, must necessarily be a precarious one; and it is a pathological fact that an organ which is badly supplied with blood is also more liable to disease, because the insufficient supply of blood causes a diminution in the number of phagocytes thereby weakening the defense of the organ against infection, as explained in Chapters III and X. Consequently the microbes easily prevail, particularly in a portion of the body like the intestines, where they normally exist in such great numbers. By the foregoing we have not only shown the cause, but also the principles for a rational prevention, of appendicitis. As we have seen, the starting point of all mischief is the close proximity of the psoas to the appendix, and the occasional cause is constipation, with stagnation of the fæcal contents. The best preventive against appendicitis consists in avoiding both causes, which, however, is only possible in the latter case by adopting all those measures we have mentioned in the chapter on the treatment of constipation. The first cause, the close contact of the psoas with the appendix, can certainly not be prevented; but what we can do is to avoid all movements by which the psoas is unduly pressed against the appendix. This can be done by avoiding those exercises in which the psoas is brought into frequent contraction and then pressed forcibly against the appendix: for instance, running, cycling, etc. The young lady, already referred to, with the large stone in the appendix, indulged freely in such sports. The habit of sitting with one leg crossed over the other should also be avoided.