The stomach, however, is the portal to a vast series of important organs, and is protected by a phalanx of sentinels, endowed with powers proportioned to the importance of the organ which they guard. There is little that falls within any idea which we can express by the term mechanical; everything is subjected to an examination essentially sentient; to powers residing in the nerves; the _laws_ and _operations_ of which, we can with proper attention trace out, but which exhibit powers demonstrative of an intensity and refinement of which our limited perceptions scarcely enable us to form a definite idea. First, there is the olfactory nerve, between which and the stomach there is the most vivid sympathy. Until our tastes become vitiated, the stomach seldom admits anything of which the nose reports unfavourably. The sense of smell, even in the somewhat measured power possessed by man, is capable of detecting forms of matter so subtle as to be beyond our powers of imagination. Nothing which so plainly deals with "matter" impresses more strongly the immense range which must exist between the chemistry of life and that of the laboratory. We all know the extraordinary powers of musk. I have myself a small mass of odorous matter (a Goa ball) which, from the circumstances under which it came into my possession, must have been emitting the odour for little less than a century. It has been exposed to air, is covered by a film of gold (I believe), is in no respect visibly changed, and for the last thirty years not detectably in weight; yet at this moment it emits as strong an odour of musk as ever. How exquisitely subtle must be the matter thus emitted; or how still more wonderful if it merely so modifies the atoms of air in its neighbourhood as to produce odour. We have no intellectual powers which enable us to realize a conception of such infinite tenuity of matter; yet the sense of smell instantly detects its presence.