756 THE POPULAR SCIENCE MONTHLY. 



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 tenaciously 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 fibrino- 

 plastic substance, or the later theory of Hammarsten, that fibrine is 

 produced from fibrinogen by the action of a special ferment. 



One function yet remains which can not be altogether omitted from 

 our consideration. This function is that of the 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 protagon, the specific characters of which have lately been con- 

 firmed by Gamgee. In function, the nerve-cell and the nerve-fiber are 

 occupied solely in the reception and the transmission of energy, which 

 is in all probability electrical. There is evidently a close analogy be- 

 tween the nerve and the muscle, the axis cylinder like the fibrilla being 

 composed of cells, and having a positive electric charge upon the exte- 

 rior surface, which has a tension of one tenth of a volt. Haughton 

 attributes tinnitus auriicm to the discharge 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 

 Muller predicted that the velocity of nerve transmission never could 

 be measured, yet Helmholtz accomplished the feat very soon after- 

 ward. His results, 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 twenty-six to twenty-nine 

 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 con- 

 ductor depends upon the production of a charge, the time of this 

 appearance 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 experiment, 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 two hundred and sixty-eight miles in an entire 

 second. Hence the marvelous discrepancies which have been observed 

 in the results of experiments made to determine the velocity of elec- 

 tricity 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 



