114 



SCIENCE. 



he showed that when a drop of water served to connect the 

 copper and the zinc, no charge at all was produced. The 

 fact may therefore be regarded as established, as the result 

 of numerous and varied experiments, that a difference of 

 electrical potential is always developed at the surfaces of 

 contact of heterogeneous media. Not only is this true of 

 solids in contact with solids, but also of solids with liquids, 

 and of liquids in contact with each other. Of course the 

 production of electricity by contact must result from a loss 

 of energy elsewhere. In the opinion of Cumming, it is the 

 loss of energy which is owing to the unsymmetrical swing- 

 ing of the molecules on the two sides of the surfaces of con- 

 tact, 'which reappears as difference of potential between the 

 solids or as the energy of electrical separation. 



But we may carry the sequence yet another step backward. 

 The energy which is thus lost at the surfaces of separation 

 must be heat, and this junction must be cooled thereby. 

 Thus the production of thermo-electricity is seen only to be 

 a special case of a general law, a view to which the well- 

 known Peltier effect gives support. In this phenomenon, 

 when two metals are joined together in the form of a ring 

 and one junction is heated, a current is produced which 

 cools the other junction. From a study of these conditions, 

 Thomson has concluded that the absorption of heat in a 

 thermo-electric circuit varies for different metals with the 

 direction of the current. Thus in iron, the current from hot 

 to cold absorbs heat, while in copper the current which ab- 

 sorbs heat is from cold to hot. In entire accordance with 

 these results, are the conclusions recently reached by Hoor- 

 weg. Whenever two conductors come into contact, motion 

 of heat results in the development of electricity, the current 

 produced existing at the cost of heat at one part of the point 

 of contact, and evolving heat at the other for a result. Hence 

 all voltaic currents are thermo-currents. 



To return to the muscle, it must now be apparent that the 

 electrical charge which appears in its fibre may have its ori- 

 gin in so purely a physical cause as the contact of the hetero- 

 geneous substances of which the tissue is built up ; the 

 maintenance of this charge being effected by chemical changes 

 going on constantly in the substance of the muscle, by which 

 the carbon dioxide is produced, which is shown to be a 

 measure of the work done. 



Conceding now, that muscular contraction is of the nature of 

 an electric discharge, by what mechanism is the contraction 

 effected ? A string of electrical masses, like a muscular fibril, 

 would seem at first to oppose the view now advauced. Such a 

 row of particles would indeed attract each other when elec- 

 trified, and shorten the length of the whole. But the force 

 of contraction would increase as the length diminished ; 

 whereas the fact in the case of the muscle is precisely the 

 reverse. Two theories have been advanced to account for 

 the result. The first, proposed by Marey, likens the mus- 

 cular fibre to a string of india-rubber which, when stretched, 

 contracts upon the application of heat, thus transforming 

 heat directly into work. The other, brought forward and 

 strongly supported by Radcliffe, explains contraction by 

 direct electric charge. Each fibre of the muscle, together 

 with its sheath, constitutes a veritable condenser, the charge 

 upon the exterior being positive, and upon the interior nega- 

 tive. When a charge is communicated to the fibre, lateral 

 compression results from the attraction of the electricities 

 of opposite name, and since the volume remains constant, 

 elongation is the consequence — precisely as a band of 

 caoutchouc, having strips of tin-foil upon its sides, may be 

 shown to elongate when charged like a condenser. In this 

 view of the matter the normal condition of the muscle is 

 one of charge, of elongation. Contraction results from the 

 simple elasticity of the muscle itself, the function of the 

 nerve being only that of a discharger. Whether this theory 

 represents the actual fact or not, in all its details, it is sup- 

 ported by the existence of rigor mortis, by the continued re- 

 laxation of muscle during the flow of the current, by the 

 cessation of contraction on the free access of blood, and 

 by many other phenomena otherwise difficult to explain. 



From this brief review, does it not seem probable that 

 the phenomenon of muscular contraction may be satisfac- 

 torily accounted for without the assumption of "vital irri- 

 tability," so long invoked ? May it not be conceded that 

 the theory that muscular force has a purely physical origin 

 is at least as probable as the vital theory? 



Time would fail me to discuss the many other phenomena 

 of the living body which have been found, on investigation, 

 to be non-vital. Digestion, which Prout said it was im- 

 possible to believe was chemical, is now known to take 

 place as well without the body as within it, and to result 

 from non-vital ferments. Absorption is osmotic, and its 

 selective power resides in the structure of the membrane 

 and the diffusibility of the solution. Respiration is a 

 purely chemical function. Oxyhaemoglobin is formed 

 wherever haemoglobin and oxygen come in contact, and 

 the carbon dioxide of the serum exchanges with the oxy- 

 gen of the air according to the law of gaseous diffusion. 

 Circulation is the result of muscular effort both in the 

 heart and the capillaries, and the flow which takes place is 

 a simple hydraulic operation. Even coagulation, so tena- 

 ciously regarded as a vital process, has been shown to be 

 purely chemical, whether we adopt the hypothesis of Schmidt 

 that it results from the union of two proteids, fibrinogen 

 and fibrinoplastic substance, or the later theory of Ham- 

 marsten that fibrin is produced from fibrinogen by the ac- 

 tion of a special ferment. 



One function yet remains which cannot be altogether 

 omitted from our consideration. This function is that of 

 Mie nervous system. In structure, this system is well known 

 to us all. In composition, it is made up essentially of a 

 single substance, discovered by Liebreich and called pro- 

 tagon, the specific characters of which have lately been 

 confirmed by Gamgee. In function, the nerve-cell and the 

 nerve-fibre are occupied solely in the reception and the 

 transmission of energy, which is in all probability electri- 

 cal. There is evidently a close analogy between the nerve 

 and the muscle, the axis cylinder like the fibrilla being 

 composed of cells, and having a positive electric charge 

 upon the exterior surface, which has a tension of one-tenth 

 of a volt. Haughton attributes tinnitus aurium to the dis- 

 charge of nerve-cells. 



The only objection raised to the electrical character of 

 nerve-energy is based upon its slow propagation. Though 

 thirty years ago Johannes Miiller predicted that the velocity 

 of nerve-transmission never could be measured, yet Helm- 

 holtz accomplished the feat very soon afterward. His re- 

 sults, like those of subsequent experimenters, show that 

 the velocity of propagation of the nervous influence along 

 a nerve, like that of electric transmission, is only about 26 

 to 29 metres in a second. But it should be borne in mind, 

 as Lovering has pointed out, that electricity has no velocity, 

 in any proper sense. That since the appearance of an 

 electrical disturbance at the end of a conductor depends 

 upon the production of a charge, the time of this appear- 

 ance will be a joint function of the electrostatic capacity of 

 the conductor and of its resistance. Since each of these 

 values is directly proportional to length, it follows that the 

 time of transmission will vary as the square of the length 

 of the conductor. While therefore, in Wheatstone's ex- 

 periment, he found that electricity required rather more 

 than one-millionth of a second to pass through one-quarter 

 of a mile of wire, it does not follow that it would traverse 

 288,000 miles in one second, as he assumed. Indeed, as 

 Lovering has shown, its actual velocity would be only 268 

 miles in an entire second. Hence the marvellous dis- 

 crepancies which have been observed in the results of ex- 

 periments made to determine the velocity of electricity on 

 long wires are explained. 



In the nerve itself, therefore, the velocity of transmission 

 may be supposed to be the less as its resistance is greater. 

 Now, Weber has shown that animal tissues in general have 

 a conductivity only one fifty-millionth of that of copper. 

 And Radcliffe found that a single inch of the sciatic nerve 

 of a frog measured 40,000 ohms ; a resistance eight times 

 that of the entire Atlantic cable. In experimenting to con- 

 firm the above law of velocity, Gaugain measured the time 

 of transmission of the electric current through a cotton 

 thread 1.65 metres long and found it to be eleven seconds. 

 Two similar threads placed consecutively, thus forming a 

 conductor twice as long, required forty-four seconds for 

 the passage of the current ; or four times as long. From 

 these data the velocity in the short thread is at the rate of 

 only 0.15 metre in one second ; and in the long one only 

 about half this rate, of course. Hence the fact that the 

 energy of nerve moves at the rate of only 28 metres per 

 second is really no proof that it is not electricity. 





