and containing membranes such as the horny layer of the skin which are formed by the living cells. The whole is comparable to citizens grouped in farms and factories subserving one or other function necessary for the commonweal; and just as the city has its transport connecting the whole, distributing food and the various products of the factories, a drainage and scavenger system taking away the waste material, and a telephone system through which operations can be ordered and co-ordinated according to the needs of the commonweal, so has the body its blood circulation, digestive and excretive systems, and a co-ordinating nervous system. How small are the cells, how infinite their number is shown by the fact that each drop of blood the size of a pin's head contains five million red corpuscles; there are five or six pints of blood in the body!

The living substance, e.g. of a nerve cell, appears as a watery substance crowded with a countless number of granules, which are so small that only the light dispersed around each is visible under the highest power of the microscope when illuminated by a beam of light against a dark ground, just as the halo of each dust particle in the air is made visible by a beam of light crossing a dark room, and just as these dust particles are in dancing motion due to the currents of air, so are the particles in the living substance ceaselessly kept dancing by the play of inter-molecular forces. From the dead substance of the cells the chemist extracts various complex colloidal substances, e.g. proteins, fats, carbohydrates, and various salts, and these in their turn he can resolve into chemical elements. The interplay of energy between the multitude of electrically charged granules inside the cell, and the environment outside keeps up the dance of life, the radiant energy of the sun, and the atomic energy of the elements being the ultimate source of the energy transmutations exhibited by both living and non-living matter.

In the living cell there is an interplay of the energy of masses of molecules forming the granules, of single molecules in watery solution, of atoms which compose the molecules, and of electrons, the various groupings of which compose the atoms of the elements. The elements themselves are now recognised to be transmutable through simplification and rearrangement of their electronic structure, and to be evolved out of one primordial electronic unit, a unit of energy, unknowable in nature, out of the groupings and transmutations of which arise all manner of living and non-living forms, the apparently indestructible stable materials being no less in a state of flux and evolution than the most unstable. The complexity of the transmutations of energy and ultimate unknowableness and mystery of their cause are no less in the case of a drop of water or a particle of dirt than in that of a living cell. The scientific conception of the universe, the very opposite of materialism, approaches pantheism.

The living substance of a uni-cellular organism, similarly the congery of cells forming the body of man, has evolved the power of sensing and of moving towards, or away from life-giving or destroying sources of energy. Special sense-organs, receptive of one or other form of energy have been evolved through the æons of the struggle for existence, together with nervous and muscular systems, to enable him to preserve his life in the midst of the shocks and thrills of his environment. There are also evolved inner senses, and a sympathetic nervous system which knits all parts of the body in harmonious action; the community of action also being brought about by the circulating fluids of the body, the blood and the lymph, to which each living cell gives and from which each cell takes. For communion with the environment, eyes for visual, and sense organs in the skin for thermal radiant energy have been perfected, ears for sound waves travelling through air, taste organs for substances in solution, smell organs for particles of substances floating in the atmosphere, touch organs for sensing movements of masses.

The receptive cells of the special sense organs are composed of watery, granular, living substance and elaborate mechanisms have been evolved for converting one or other form of energy into such a form that it can be received by the living substance, e.g. the intricate structure of the eye with its focussing lenses, retinal cells laden with pigment sensitive to light, the ear with its drum membrane vibrating in unison with sound waves in the air, its chain of transmitting osicles, and complicated receiving organ placed in the spiral turns of the cochlea. Be it noted, the receptive cells of the sense organs are immersed in fluid, and each sense organ is specifically sensitive, i.e. only to that form of energy which it has been evolved to receive through countless ages of evolution.

The nervous system is composed of myriads of nerve cells, and of nervous fibres, which are long and exceedingly slender processes of these cells formed of similar substance, each shielded and insulated by a double coat. The nerve cells and the nerves are arranged in an ordered plan which has been unravelled by ingenious methods. They connect all parts of the body one with another. Think of the whole telephone system of Britain linked up together with millions of receivers, thousands of local exchanges, hundreds of central exchanges, etc., the nervous system with its sense organs, sensory nerves, lower and higher nerve centres and motor nerves, is infinitely more intricate than that. The whole forms an interlacing feltwork formed of watery nerve cells and processes, and not only receives sensory stimuli and transmits them as motor impulses, but is more or less permanently modified by each sensory thrill which enters it, memorising each, more or less, for longer or shorter time according to its character or intensity. Thus the response of the nervous system to sensory excitation changes with education, habits form and character develops from birth to manhood, to decay again from manhood to old age, ceaselessly changing, but becoming graved on a certain plan. The making thereof depends on inborn qualities of the living substance—the conjugate product of the male and female parents, this moulded by environmental conditions, both in utero and after birth, by food, and the ceaseless instreaming of sensations. Depending on the nutrition of the cortex of the great brain, abrogated by narcotics, absent in sleep, consciousness of our being flickers from moment to moment, the product of the instreaming of sensations from the outer world and from our own body, and of memories of past sensations, aroused, by some present sensation. Conscious judgement arises from the balancing of present sensations with memorised sensations and leads to purposeful actions.

Beneath the conscious world an infinite host of functions are carried out unconsciously, functions depending on the nervous connection of one part with another, just as the common people carry out a host of actions through the telephone system without the cognisance of the government which is seated at the highest central exchange.

To find food, satisfy the sexual instinct, escape enemies, gain shelter from excessive physical changes of environment, the special senses and nervous system have then been evolved and perfected in the intricacy of their mechanism through vast æons of evolution. There is evidence that man has for some million years trod the earth; but the senses of sight, hearing, smell, taste, touch were evolved in the vast procession of lower animals which preceded him for those millions of years which reach back and ever back to the first generation of life.

The realisation of these facts saves the physiologist from being deceived, either by fraudulent tricks or those