October 1, 1897.] 



KNOWLEDGE. 



231 



which inference ia involved ; but there is a region in which 

 we must recognize hypothesis as absolute — a region below 

 the surface whence no reflected light can pass, but whence all 

 observed phenomena proceed. It would appear that the 

 dissemination of the minute particles of musk is due to a 

 propulsive energy, and this must be an intermolecular 

 force which we can best conceive as motion — motion in 

 such excess of the intermolecular attraction as to expel 

 from the musk the molecules that are upon the surface. 

 The relation of heat to the emanation of odours 

 strengthens the belief that intermolecular motion is the 

 form in which the energy exists that expels the molecules 

 from the mass and propels them through the air. 



In all substances there seems to be an attraction among 

 the molecules which unites, and a peculiar motion which 

 tends to separate, and these two opposing forces may be 

 very unequal or nearly balanced, and we have accordingly 

 a very stable substance or an unstable one. For example, 

 yellow phosphorus cannot be in contact with air without 

 oxidizing — it gives ofl" white fumes, burns slowly, and 

 forms phosphoric anhydride, the atoms at the surface 

 joining those of the oxygen in the air ; there is, as it ware, 

 among the individual molecules of phosphorus a keen 

 desire to leave the family circle. In the case of carbon 

 we have a condition of things not far removed, compara- 

 tively, from that of phosphorus ; the motion which tends 

 to separate the molecules of carbon has to be increased 

 by adding that of heat before the attractive force can be 

 overcome. So also in the explosion of a mixture of coal-gas 

 aud air, the effect of a spark on gunpowder, or the simple 

 added motion of concussion in a quantity of nitro-glycerine 

 — all these are examples of the disturbance of chemical 

 equilibrium by added motion, which, so to speak, sets up 

 the necessary rhythm among the molecules — beats time 

 to enable them to keep step with their companions in the 

 new combinations formed. 



We have long been accustomed to ascribe the mani- 

 festation of energy by muscles to chemical combination — 

 latent chemical energy. It is conveyed into the body 

 by food on the one hand, and oxygen on the other ; the 

 food comes directly from vegetable and animal life, but 

 all is ultimately traceable to the former. In growing 

 plants, simple compounds — especially carbonic acid and 

 water — are broken up under the influence of light and heat. 

 The light and heat are essential in order to promote 

 chemical change, and the evidence is conclusive that they 

 — light and heat — disappear in the process : that is, the 

 minute motion tears asunder the carbon, oxygen, and 

 hydrogen, and to do this it has to pass into the molecules 

 of their elements and it remains in them — slowed down, so 

 to speak. This process in the phnit is reversed when 

 chemical union occurs in the animal body, in which vege- 

 table tissue is burnt as in a furnace. The original simple 

 compounds — carbonic acid and water — are reproduced : 

 that is, solid carbo-hydrates are gasified, and the energy 

 that was hidden ia revealed and partially released — the 

 motion of the light and heat passes between the atoms of 

 the elements that are separated, and remains until the new 

 conditions permit its liberation. It is the sunshine, near 

 or distant, recent or long ago, which constitutes the 

 source of the energy — which, in fact, is the energy— mani- 

 fested in animal life ; and we get, in a sense, second-hand 

 sunshine by the combustion of coal — decomposed vegetable 

 tissue. 



It is one of the most familiar facts of physiology that all 

 muscular action is accompanied by chemical changes, by 

 the formation of simpler chemical compounds than those 

 which constitute muscular tissue, and especially by the 

 formation of carbonic acid in combustion. The stimulus 



which makes a muscle contract may be conceived as 

 motion and as (idded motion, the effect being like that which 

 makes a fire burn or gimpowder explode. As the lighted 

 coal goes on burning because the released motion of heat 

 acts as a stimulus to the adjacent molecules — increasing 

 this motion so as to release them — so the released motion 

 in muscular contraction acts as a stimulus which is pro- 

 pagated with intense rapidity along the fibre comparable 

 to that which occurs in a gas or explosive substance. 

 It is often said that protoplasmic substance has a property 

 of contractility, a peculiar result of life. In muscle there 

 is only a change of shape, not of size, and there is no real 

 drawing together ; alike in a muscle and in an amn'ba, the 

 change is the result of some external stimulation, a form 

 of energy — that is, of motion. May the process not be the 

 same in each case — simply a release of atoms and a release 

 of motion by added motion, definite in character, in relation 

 to the place, character, and degree of the added motion 

 which excites it '? 



In living tissue we may, conceivably, have other forms 

 of motion than those we meet with in inorganic matter. 

 But we are only justified in assuming the unknown when 

 it is certain that the known is inadequate. The nature of 

 nerve force is unknown, but it is capable of propagation 

 along a nerve fibre, and, this being so, it must be either a 

 thing moved or a form of motion. Can we form any con- 

 ception of the nature of the motion, if, indeed, it be a form 

 of motion '? A pretty conception of the nature of nerve 

 force is its resemblance to electricity, a nerve fibre being 

 like an insulated wire, and the nervous system a com- 

 plicated electric battery, the circuit of which may be 

 completed by the touch of a hair, the hum of a bee, the 

 scent of flowers, and so on, so as to transmit messages to 

 the brain. All the facts we know regarding the production 

 of nerve energy show that it is attended by chemical com- 

 bination such as that which accompanies muscular con- 

 traction. Nerve.tissues are the most elaborate, unstable, 

 and delicately equipoised of all the tissues with which we 

 are acquainted. Does it seem strange that conduction so 

 rapid as we know that of nerve force to be, should be a 

 result of chemical action '.' Think of the rapidity with 

 which a train of nitro-glycerine will explode, and the chief 

 part of the difliculty vanishes. We thus conceive that the 

 transmission of nerve energy is the conduction of released 

 motion by means of propagated chemical action along the 

 molecules of the fibrils. 



The force which turns a delicate chemical balance may 

 be minute, but think what takes place when the lightest 

 touch of a hair upon the skin of the leg acts on the brain 

 and is perceived ! Such delicate equilibrium exists 

 between the motion of the atoms and their restraining 

 attraction, that the motion of the hair, added to that 

 already present, releases atoms and releases their super- 

 fluous motion — comparable, in a way, to the shivering of 

 a sheet of glass into a thousand fragments by touching it 

 with a red-hot wire. This instability of nerve tissue may 

 be due to the presence of phosphorus, an element which, 

 as we have noted, has naturally an atomic motion in 

 excess of its restraint ; its presence may alone make the 

 motion almost equal to the restraint in the living tissue of 

 which it forms part, so that the least disturbance will set 

 molecules free something after the fashion of the dissemi- 

 nated musk. 



The motion of the nerve impulse disturbs by its addi- 

 tion the preceding equilibrium and increases the motion in 

 the structures that receive it, so that in them it exceeds 

 the attraction, and there is proportional release of atoms 

 and of energy. Throughout the nervous system, from the 

 sensory periphery, on which external energy acts, to the 



