Memory. 681 



sorts of facts are accumulated better in youth. It also shows the cor- 

 relation between large cerebrum and long period of youth, maturity 

 coming early to those animals whose capacit} r for absorbing facts is 

 soonest exhausted. Protracted use of the cerebral cells, on the other 

 hand, tends to perpetuate their youth and plasticity, so that a person 

 who has been a student all his life can learn more at 50 than one who 

 has been no student can do at at 30. 



In order to produce a sensation some molecular change must be made 

 in the cells of the cerebral cortex corresponding with the sense organ 

 under stimulation. If the cortical center for visual sensations, for ex- 

 ample, is for an}' reason not in working order, an object before the eye 

 makes its impiession on the retina, but produces no sensation, and, as 

 Ferrier observes, the apparatus is like a camera without the sensitized 

 plate ; the cortical cells, when in normal condition, being comparable to 

 a chemically prepared sensitized plate, on which the energetic rays pro- 

 duce a chemical change. 



Consciousness in the lump, and as we generally speak of it, is simply 

 an aggregate of sensations, some of which may be fresh from the ex- 

 ternal sense organs, but the bulk of them, especially in old and well de- 

 veloped brains, are usually the revivals of memories. The larger the 

 cerebrum the more do the memories registered in it enter into the stim- 

 uli which direct motor action. The cerebral influence is small in a fish. 

 Among the mammals it progressively increases up to man, in whose case 

 it has, from long race habit, become so disproportionately great, that the 

 loss of the cerebrum would make in his actions a far greater relative 

 difference than such loss would in any of the lower vertebrates. Fol- 

 lowing this habit of action there has come about a much greater depend- 

 ence of the motor organs upon the cerebrum for their control and di- 

 rection. In all vertebrates the loss or destructive lesion of the motor 

 centers of the hemispheres, is followed by complete paralysis of the 

 muscles as to purposive or cerebral stimulation, that is, volitional ac- 

 tion, and the possibilities of reflex action are all that remain. In the 

 case of man, these possibilities, relatively to those of his normal state, 

 are very small, while with the lower vertebrates they are large. A fish 

 devoid of his cerebral lobes, still performs many intricate and well co-or- 

 dinated movements. In the case of man, the cerebral organs have 

 gained such a relative preponderance over the lower ganglia, and so far 

 superseded them in many of the common activities, that their loss, or 

 atrophy, often makes him more helpless than the lowest animals. 



