RHYTHM 



duly distended. But after many hours of activ- 

 ity the ratio of repair to waste is sensibly di- 

 minished ; there is a fall in the average chemical 

 instability of the cerebral nerve-molecules, and 

 a consequent diminution in the amount of cere- 

 bral stimulus ; until presently the amount of 

 stimulus sent up from moment to moment 

 along the cervical branch of the sympathetic 

 nerve exceeds the amount which the cerebrum 

 can oppose to it. Experiment has shown that 

 the effect of stimulating the sympathetic nerve 

 is to contract the muscular walls of the cerebral 

 arteries. The supply of arterial blood is thus 

 so far diminished that consciousness ceases. 

 But now the other half of the rhythm begins. 

 The cessation of conscious activity greatly di- 

 minishes the waste of cerebral tissue — and, 

 although repair is also somewhat lessened by the 

 lessened blood-supply, yet the ratio of repair 

 to waste is increased. The complex nerve- 

 molecules are built up to higher and higher 

 grades of instability, until it only needs a slight 

 stimulus from without, in the shape of a sensa- 

 tion of sound or of light or of touch, to elicit a 

 discharge of nerve-force from the cerebral gan- 

 glia. This discharge is instantly answered by a 

 rush of blood, which distends the cerebral arte- 

 ries, revives consciousness, and holds in abey- 

 ance the contractile energy of the sympathetic 

 nerve, until the decreasing ratio of repair to 



VOL. II 177 



