496 



SCIENCE. 



[N. S. Vol. XV. No. 378. 



passage of the particles from the solution 

 to or toAvard the gel, and that if we can 

 prevent gelation stimulation is prevented 

 and irritability is lost. This is indicated 

 by the following facts among others: 



The nerve contains colloids. Colloidal 

 solutions, the particles of which cany posi- 

 tive charges, are precipitated by negative 

 ions. Nerve irritability is increased by 

 cooling and diminished by warming. The 

 stability of the hydrosol is probably dimin- 

 ished by cold and increased, like common 

 gelatine, by moderate warmth. Also when 

 coagulation by heat occurs the nerve is 

 stimulated. Coagulation is but the forma- 

 tion of an irreversible gel. Darwin 's obser- 

 vations on Drosera and other plants by 

 optical evidence demonstrates also this 

 gelation. Darwin observed in his work on 

 ' Insectivorous Plants ' that the passage of 

 the impulse over plant cells, which corre- 

 sponds to the nerve impulse in animals, 

 was accompanied by a visible precipitation 

 or gelation of the protoplasm, the nature 

 of which he did not understand, but which 

 he called aggregation. He states that the 

 molecular change supposed to occur in 

 nerves may thus actually be seen in plant 

 cells. There can be no doubt that he was 

 right in comparing this change to the nerve 

 impulse. He found that it was produced 

 most readily by the citrates and phos- 

 phates, and was checked by Ba, K and 

 other such salts. Thus his facts correspond 

 closely with those I have found for the 

 nerve. Aggregation was prevented by 

 ether, by CO, or lack of oxygen. It could 

 be produced by the extraction of water. 

 His description of the process leaves little 

 ■doubt that he is describing the formation 

 of a reversible gel. The aggregated par- 

 ticles afterwards dissolved. The action of 

 ar ?thetics and the electrical phenomena 

 cf the nerve also support the idea that stim- 

 ulation is a process of gelation. This will 

 be discussed later. 



These facts indicate the truth of the fol- 

 lowing general statements: 



I. Protoplasm consists essentially of a 

 colloidal solution, the particles of which 

 are positively charged. It is a reversible 

 hydrosol. 



IT. Stimulation consists in the passing 

 of the solution to or toward the gel. Irri- 

 tability is reduced or abolished if we make 

 the sol state more stable, or if gelation is 

 complete. In other words, irritability 

 varies inversely with the stability of the 

 hydrosol. 



9. Electrical stimulation. If stimulation 

 is due, as I believe, to the negative charges 

 the ions bear and is prevented by the posi- 

 tive, the identity of electrical and chemical 

 stimulation is thus demonstrated. It 

 makes no diffei-ence whether we put the 

 negative charges into the nerve on ions or 

 whether by touching the nerve with elec- 

 trodes we bring about, so to speak, a sxir- 

 plus of positive charges at one pole and 

 negative at the other. The end result is 

 the same. It is thus plain why the stimu- 

 lus begins at the negative electrode, or 

 kathode. In this region by the action of 

 the kathode, the negativity of the nerve is 

 increased and gelation occurs. In what 

 manner this negativity is increased will be 

 discussed in the full paper, but it may be 

 'diie indirectly to the hydroxyl ions. Elee- 

 trotonus is also explained. By the pas- 

 sage of the current the negative charges are 

 in excess or preponderate in their action 

 near the kathode and positive charges pre- 

 ponderate near the anode. The stability of 

 the hydrosol is diminished near the former 

 and increased near the latter. Irritability 

 is altered as just explained. These conclu- 

 sions are supported by Hardy's obseiwa- 

 tions on the movement of colloidal particles 

 in the electric current and their precipita- 

 tion at the kathode if positively charged. 

 If the nerve is already near gelation (very 

 irritable by cold or drying) we may have 



