64 PROCEEDINGS OF THE COTTESWOLD CLUB 



the }jhenomenon of winter sleep, in which hfe is preserved, 

 though there is a temporary lowering of the metabolic 

 processes ; or when the metabolic processes of the 

 organisms do not enter into abeyance, we find the remark- 

 able phenomenon of migration, as is the case with many 

 birds. 



NOTES 

 Re •■ IRRITABILITY 



MovciiieiU ol a voluntary dcsLrijition is accomplished liy muscles receiving; tliioujjli 

 nerves their stimulus to action from the brain, which in turn is stimulated in an unknown 

 way by the will. Thus the central nervous system is both the terminus to whicli 

 messages from the organs of sense are sent, and that from which commands to the voluntary 

 muscles proceed. 



All sensory function is not sensation, and all movement is not voluntary. The nervous 

 system may receive an influence from without and transmit it to groups of muscles 

 without intervention of any act of consciousness. Tiiis is what is called reflex action, and 

 in such a case the part irritated, from which the nervous impulse starts, is still said to have 

 sensibility and the nerve to he sensory, although there is no sensation, and the movement 

 is involuntary. Also the jjroperty of res])onse to irritation is not confined to the nervous 

 system ; structures may alter their shape or undergo other change on aj)pIication of a 

 stimulus, and this ])ropertv is termed irritability. The active part of change of shape or 

 movement probablv m all cases consists in contraction, and is hence called contractility. 

 Irritaliility and contractility, although they may be well included under the terms sensory 

 function and movement, are not, like sensation and voluntary movement, conhned to 

 animals. They are found in the vegetable world also; and it may be maintained with 

 probability, that they are j)roperties of every part of every living being. — Cleland's 

 "Animal Physiology," pp. 15, 16. 



The great majority (if not the whole) of the moven'lents of the body and its j)arts are 

 the efl'ect of an influence i, technically termed a stimulus or irritation) applied directly, or 

 indirectly, to the ends of afl'erent nerves, and giving rise to an molecular change, which is 

 propagated along their substance to the central nervous organ with which they are 

 connected. The molecular activity of the afferent nerve communicates itself to the central 

 organ and is then transferred to the motor nerves which pass through the central organ 

 to the muscles aflccted. And when the disturbance in the molecular condition of the 

 arierent nerves reaches their extremities, it is communicated to the muscular fibres and 

 causes them to take up a new position, so that each fibre shortens and becomes thicker. 

 Such a series of molecular changes is called a reflex action, the disturbance caused by the 

 irritation being as it were reflected back, along the motor nerves to the muscles. 



A reflex action, strictly so called, goes on without our knowing anything about it, and 

 hundreds of sucli actions are going on continually in our bodies without our being aware 



of them We speak of " states of consciousness," but what consciousness is, 



we know not ; and how it is that anything so remarkable as a state of consciousness comes 

 about as the result of irritating nervous tissue, is just as unaccountable as any alternate 

 fact of Nature.' — Huxle)', "Elementary Lessons in Physiology," pp. 187, 18B : see also 

 p. 254, &c. 



