THE BASIS OF LIFE 11 



parts retracted, in the search for food. Such movement 

 is a response to stimulus. Stimuli received at one part of 

 the body-substance are transmitted to another. The body- 

 substance is irritable. It acknowledges stimuli ; it conducts 

 them. But if the amoebae are watched until, owing to lack of 

 oxygen or other cause, they die, their irritability comes to an 

 end. It is a phenomenon of life. Again the physiologist is 

 in a dilemma. Either protoplasm is not protoplasm when 

 death has supervened, or protoplasm is not irritable as such. 

 It is somewhat paradoxical to ascribe to the physical basis of 

 life a property which depends upon its being alive. 



Yet the influence on protoplasm of anaesthetics makes it 

 difficult to understand how it can be either physically or 

 chemically a substance which loses its form or changes its con- 

 stitution whenever it ceases to display the usual evidences of 

 its existence. Chloroform and similar agents suspend irrita- 

 bility. Yet irritability returns as their influence passes off. 

 They appear to hold it in check without at any rate visibly 

 changing the nature of the irritable substance. 



All parts of the minute body-substance of an amoeba are 

 equally irritable. In higher animals irritability is concen- 

 trated in the nervous system. The form of irritability to 

 which consciousness is adjunct is restricted to the cortex of 

 the great brain. 



Chloroform and similar agents are termed " anaesthetics " 

 because they abolish the irritability of the cortex of the great 

 brain, before their effects upon other parts of the nervous 

 system are sufficiently pronounced to endanger the working 

 of the animal machine. Pain ceases to be felt before the dose 

 of anaesthetic is sufficient to suspend the irritability of the 

 centres of reflex action. All protoplasm, whether animal or 

 vegetable, is susceptible to the influence of these agents. 

 They cause it to enter into a state which resembles death in 

 all respects save the impossibility of revival. There is a great 

 demand in the Paris flower-market for white lilac in the 

 winter. The plant cannot be forced until after a period of 

 rest. By withholding water and placing the bushes in a cool, 

 shady place, horticulturists endeavour to send them pre- 

 maturely into their winter sleep. Recently it has been found 

 that from three to four weeks can be gained by placing the 



