THE NERVOUS SYSTEM 305 



weakening of the circulation through the brain. Recovery 

 is brought about by placing the head on a lower level than 

 the body, so that the blood may run to the brain with less 

 exertion on the part of the heart. A violent blow on the 

 head may make one insensible at once. By breathing chlo- 

 roform, ether, or carbon dioxid, by taking morphine, the 

 quality of the blood may be so altered as to bring sleep. In 

 order that the brain may act, it must be con- 

 stantly aroused by impulses from the outer 

 world. There is a case reported of a man 

 all of whose sensory nerves had lost sen- 

 sibility except in one eye and one ear. He 

 fell asleep immediately if the . remaining 

 sense organs were closed. The conclusion 

 to be drawn from the foregoing facts is, 

 that a man loses consciousness so soon as 

 his cerebral hemispheres cease to act ; but 



his heart and lungs keep at work. It is _ 



FIG. 203. Micro- 



curious that touching the cerebrum, or scopic Diagram of 

 stimulating it with electricity, when it has cJ^^J^Jj 

 been exposed by accident, arouses no sen- Brain. 

 sation, although this organ is believed to A, external layer of as - 



. . . . ,_,. . .. . sociation cells, axons, 



be the seat of consciousness. This fact is anddendrons; B, Py - 



of great interest, for it shows that impres- 



sions coming from the sense organs alone the la y fir of medul - 



lated fibers C. The 



enter into consciousness. dendrons of the Py - 



563. Effect of removing Cerebrum. la^" 11 

 After destruction of the cerebrum, an ani- 

 mal may continue to live if fed by hand. It can run about, 

 and swallow food placed within its mouth. It will be dis- 

 turbed by a loud sound, such as the blowing of a horn. 

 It might avoid a bright flame if placed in its path, but would 

 go stupidly against other objects ; but it is idiotic, for all 

 acts of intelligence cease. Its time is spent in sleep or 

 mechanical wandering. A frog having its cerebrum re- 



