NERVOUS SYSTEM 237 



force that draws steel to steel, and directs the compass needle's 

 point, all, like the colours in the spectrum of a light-ray, spring 

 from a single source, all are blended together in one unquench- 

 able, all-pervading power ". 



Huschke, 1 too, has likened the brain to a great electric 

 battery. The two hemispheres are the plates which generate 

 the cerebro-electric current, the commissures the fluid of the 

 battery, the centre and poles are in the convolutions, and the 

 wires of the circuit the peduncles. The chemical process set 

 up by the electric current is the process of oxidation. In the 

 cerebellum Huschke sees an indifferent point in the vermiform 

 process, the fluid conductor in the pons, while the crura cerebelli 

 are the wires. 



Even the best apparatus, the most perfect machinery, wears 

 out in time, so the animal or human brain requires certain 

 periods of rest, i.e., sleep, if it is not to be seriously and pre- 

 maturely injured. The sleep of the domestic animals varies 

 considerably. In horses it is extraordinarily light ; in cattle, 

 cats and often in dogs it is deep and sound. 



This deep sleep of animals and man represents a condition 

 comparable to that produced in animals by experimental re- 

 moval of the cerebral hemispheres when neither perception of 

 sensory impulses nor voluntary movements take place, only 

 automatic and reflex movements, such as respiration and the 

 heart beat, being possible. The physiological sleep of normal 

 animals and man (averaging in adults six to seven hours) has 

 in former times met with the most diverse explanations. 



Even at the beginning of the nineteenth century one ex- 

 planation given was the evaporation of the nerve-spirit from 

 the blood, another was syncope of the vital process. Sequard 

 regarded sleep as a daily recurring epileptic seizure. In later 

 times sleep is considered as the result of a hyperaemia or an 

 anaemia of the brain, of a deficiency of oxygen in the blood, 

 and finally of certain products of fatigue in the blood, especially 

 lactic acid (Ranke). But all these views and theories have been 

 displaced by recent scientific research. 



It has now been definitely established that sleep is a purely 

 physical process. Formerly it was supposed that there was 



1 Huschke, loc. cit., p. 168. 



