A second aspect of the matter of material of physiology is classed as physical. This as pect of the science discusses function as motion, in short. Motions are of two kinds in living matter as in other kinds of matter, namely molecular and molar. The term molecule means little to-day with the decadence of the term atom, but nonetheless the word is in universal use, and stands in physiology for those attrac tions and repulsions which, viewed from a somewhat different angle, we term chemical. Metabolism is molecular movement, so are heat and light, electricity, nerve-force, and all those processes which to-day are on the border line between physics and chemistry. The energies of the body, in short, are reducible to modes of molecular movement. Unless we insist on vital processes as something distinct, the mole cular movements of living matter, so far as we can see, are no different from those of non living matter, except in one fundamental par ticular, namely their complexity, and this differ ence does not always obtain.
Molar movements may of course, for the sake of logical completeness, be classed as properly organic and as merely passive. The organic movements proper are again divided into two kinds, the first being muscular or active movements, and the second recoil or passive movements. It is worth noting that muscle is the sole organ for active movement in organism, although its precursors include such processes as cell-turgor, protoplasmic streaming, and even various grades of direct contractility and possibly of expansion, pro duced by various forms of contractile threads. Muscular movements are classed as vegetative and as voluntary or personal, although these, like everything else, merge more or less in sensibly into each other in the living organism.
The recoils are passive and include such essential movements as the probable passive mechanical constriction of the arterioles, of the lungs, of the urinary bladder, in short of any distended viscus. The torsional recoil of the costal cartilages is obvious in one's mind, as well as others of still less importance. Some of these recoils are made more of than fact sanctions, in all probability; even the most im portant of them all, the constricting process of the arterioles, may prove to be, after all, an active movement, and not a mere passive me chanical recoil. Molar movements have as their qualities: first, quantity, referring to the mass of active muscle concerned in them; second, extent, referring obviously to the amount of linear space involved in a short ening of the muscle; third, speed, which means the amount of space covered in a unit of time; fourth, location, which has importance in the applied science of kinesiology and in general physical education; fifth, force, which m this case means the capability of overcoming resist ance and not necessarily through space (here, pure physics has for once shown the inadequacy of some of its old definitions) ; sixth and lastly, duration.
It would be pedantic for any physicist to claim that the processes of an organism which he might care to class as ((physical)) did not merge over a considerable area with those that are more often called ccheinical.D Protoplasm includes so much, that at present to say what of its processes are physical and what chemical would be pure arbitrariness, just as both the botanists and the zoologists still include certain infusoria in their tectonic schemes.
The chemical processes of living matter, in many cases, are indescribably, and so far as we can see, unimaginably, complex. So far as we can realize at present, this may be their chief difference from inorganic chemism. In addi tion to these intricate chemical reactions of attraction and repulsion between the atoms, of course all the simpler ones are going on uni versally. Every organism is a marvelously com plicated chemical laboratory where untold multitudes of complex substances are made and unmade and intermixed; every organ is such a laboratory; some have even ventured to suggest that every cell carries on essentially this same complexity of chemic work. As an index of this intricacy of chemism, one need only to be re minded that the molecular weight of some of the component compounds of protoplasm is probably at least 150,000. As some biologist long ago suggested, it may well be that in this complexity and perhaps characteristically so, lies the secret of Life; in other words, that the living molecule lives because it is more complex and more intricately unstable than is any other substance.
A few years ago, in many of the medical schools of mark at least, there was plain a tendency to give up to biochemistry the more narrowly chemical functions of organism and to think of physiology more and more as a science of physical reactions. Then about this time we began to have an inkling of the un parelleled importance and influence of the products of the ductless glands, and, as one might expect would have happened, this stimu lated anew the former absorption in chemical physiology. At the present time, therefore, a considerable proportion of the research work being done in the laboratories of physiology is chemical in its relations and aims. One might almost say that various aspects of metabolism was at present the chief research-problem of physiology, however unfortunate for the sounded dignity of physiology such a condition of things may be. Certainly the only reason that biochemistry does not claim its own and insist that physiology attend to its more prop erly own affairs, comprehending the functions of protoplasm as a whole, is that modern chemistry plainly already has very much more than it can attend to by itself. There is room for the relatively unexpert chemic research of the physiologist, as the medical school knows him.