_Use of the Spleen._--The SPLEEN, from being an organ common to the human frame, must have an allotted service to supply; although considered useless by some, to all of unknown utility, it may be _a lateral channel of arterial blood direct from the heart, to supply the vessels lying in a portion of the body not traversed by the arteries belonging to the great arterial system_; those of the diaphragm first; thence through the umbilical cord to the fetus, in which the circulation is indispensable, from being the only means of conveying and dispersing throughout the body, in the absence of respiration, the minus-pressure matter which the organism of the fetus requires to promote the several functions, without which life would become extinct if commenced. In this supply of motion promoting elementary matter, consists all that can be considered _aeration_ of the blood, and all that the blood of both the fetus and the _adult_ requires, or can possibly receive. In the chirping chick, while within the yet unbroken shell, aeration is _prevented_ by incubation of the mother bird; but the arterialising elementary matter is amply provided within the larger, apparently empty, end of the shell. To keep out electric matter, which would exclude the blood-moving medium, is the object of the hen sitting on the eggs, and oven-hatching is effected on the same principle. _How the Diaphragm Is Raised._--The _diaphragm_ cannot rise of itself, and has no self-acting, self-lifting nerves or muscles, all flesh being composed of _inert_ atoms. The rise is proof positive that pressure is greater on the posterior than anterior surface of the membrane, and the unchanged normal pressure beneath indicates reduced pressure above; the latter is promoted by minus-pressure matter imparted by the splenic blood to the diaphragm, while passing through the vessels of the diaphragm. This arterialising matter being highly evanescent, escapes from the diaphragm and upwards, and during the escape mitigates the pressure, intercepts it in some degree from the superior surface; then, by the normal pressure beneath, the rise of the diaphragm is effected. As the escape, or separation, is becoming complete, the equilibrium is being restored, and the diaphragm depressed to the normal level. If this be not the rationale of diaphragmatic motion, it will be little improved by the substitution of muscular energy, leverage, or muscular vitality, while leaving out _muscular inertia_, which should not be omitted, but included, in accounting for every muscular action and motion. CORRELATIVE ELEMENTS. Any pair of the general elements, the interstices of one of which are the only interstices for receiving and retaining the atoms of the other, or that can be occupied by the atoms of any other of the general elements, such elements are correlatives.