4 88 SCIENCE PROGRESS 



experimental facts render a consideration of this possibility 

 necessary. Here the chemical side is not so obvious, since 

 we may suppose these molecules to have been pre-existent 

 within the cell, and to be liberated not from a position of 

 chemical combination, but from some position of physical 

 restraint on arrival of the nervous impulse. This is a 

 possibility with an important distinction. The whole sudden 

 energising of the cell is made to take an entirely physical 

 form. In this case, however, the chemical side must not be 

 lost sight of. We must suppose that, during its rest from 

 secretion, the chemical energy of the cells was utilised in 

 producing this physical condition of restraint, and so feeding 

 a secondary source of energy conveniently available at the 

 moment of stimulation. 



And now, having prepared the way by means of allegory, I 

 would turn to the specific instance which I am more concerned 

 in protecting from this purely chemical conception of function. 

 If living material is at one time stable and unstable, is labile, 

 where is this fact more obvious than in the case of nerve? 

 Excited by almost every slight change of environment to a 

 display of function and therefore most unstable, but recovering 

 so rapidly that within one five-hundredth of a second it can be 

 provoked to an exactly similar change of state — a process which 

 under favourable conditions can be repeated from dawn to dewy 

 eve without giving rise to any trace of fatigue. Pancreas cells 

 may be unexcited to their specific function save on the addition 

 of certain specific chemical materials. Mammary-gland cells 

 may preserve a similar scorn for fleeting change. In them 

 obvious chemical work is done, and the chemical composition 

 of the media in which they lie is their main concern, of which 

 they are not oblivious ; but of their extreme lability what proof 

 have we ? Astonishing pictures of exhausted cells indeed form 

 evidence for an opposition. Turn to nerve-fibres and the facts 

 are curiously reversed. Most stable and yet most unstable, 

 " labilissimi," what proof have we of the primary importance of 

 their chemical constitution and its changes ? Practically none. 

 I shall escape impeachment for this statement. The main fact 

 is so clear notwithstanding some slight evidence to the con- 

 trary. Thus Waller has in most ingenious fashion shown that 

 prolonged stimulation leads to just such a modification of con- 

 duction as is producible by carbonic acid, but not unproducible 



