246 SYMBIOGENESIS 



the additions and abstractions of molecular vibration, which in our- 

 selves produce sensations of heat and cold, produce in all creatures that 

 have nervous systems certain nervous disturbances disturbances which, 

 as in ourselves, are either communicated to the chief nervous centre, 

 and there constitute consciousness or else result in merely physical 

 processes that are set going elsewhere in the organism. In special parts 

 distinguished as organs of sense, other external actions bring about 

 other nervous re-actions that show themselves either as special sensa- 

 tions or as excitements which, without the inter- mediation of conscious- 

 ness, beget actions in muscles or other organs. Besides neural discharges 

 that follow the direct incidence of external forces, there are others ever 

 being caused by the incidence of forces which, though originally external, 

 have become internal by absorption into the organism of the agents 

 exerting them. For thus may be classed those neural discharges that 

 from moment to moment result from modifications of the tissues wrought 

 by substances carried to them in the blood. That the unceasing change 

 of matter which oxygen and other agents produce throughout the system, 

 is accompanied by a genesis of nerve-force, is shown by various facts 

 by the fact that nerve-force is no longer generated if oxygen be with- 

 held or the blood prevented from circulating ; by the fact that when 

 the chemical transformation is diminished, as during sleep with its 

 slow respiration and circulation there is a diminution in the quantity 

 of nerve- force ; in the fact that an excessive expenditure of nerve-force 

 involves excessive respiration and circulation and excessive waste of 

 tissue. To these proofs that nerve-force is evolved in greater or less 

 quantity according as the conditions to rapid molecular change through- 

 out the body are well or ill fulfilled, may be added proofs that certain 

 special molecular actions are the causes of these special re-actions. The 

 effects of alcohol, ether, chloroform, and the vegeto-alkalies, put beyond 

 doubt the inference that the overthrow of molecular equilibrium by 

 chemical affinity, when it occurs at certain places in the body, results 

 in the overthrow of equilibrium in the nerves proceeding from these 

 places results, that is, in the propagation through these nerves, of 

 the change called a nervous discharge. Indeed, looked at from this 

 point of view, the two classes of nervous changes the one initiated 

 from without and the other from within are seen to merge into one 

 class. Both of them may be traced to metamorphosis of tissue. 



Thus we see that systematic contact with the external 

 world and the necessity to vibrate, as it were, in tune with the 

 biological world le besoin, pere de 1'adresse plus response 

 from within, may be said to be responsible for the genesis of 

 the nervous system and so of organic consciousness. It is clear 



