THE NERVOUS SYSTEM 175 



a violently excessive action of the cerebral neurons starts 

 at the part irritated and passes to involve more and more 

 of the brain. In such fits it is found that at first the 

 patient's consciousness is not lost, but that, when a suffi- 

 cient area of brain is involved in this excessive and unco- 

 ordinated action, consciousness disappears. 



The study of the action of drugs which abolish, conscious- 

 ness e.g. chloroform and morphine on the dendrites of 

 brain cells, suggests a physical explanation of the loss of 

 consciousness. It is found that these drugs cause a general 

 extension of the gemmules of all the dendrites ; and, if we 

 imagine that the co-ordinated action of any part of the brain 

 is secured by definite dendrites of one set of neurons coming 

 into relationship with definite dendrites of another set of 

 neurons by their gemmules, the want of co-ordinate relation- 

 ship established by the general expansion might obviously 

 explain the disappearance of the definite sensations which 

 constitute consciousness. 



It is manifest that the range of consciousness must neces- 

 sarily be wider where the stored impressions are most 

 abundant, and where the present stimulus most readily 

 calls into action these previous lines of cerebral activity. The 

 storage of impressions is the basis of MEMOKY, the power of 

 associating these stored impressions with the present stimu- 

 lus is the basis of RECOLLECTION. It is the implication 

 of consciousness in this part of brain action which is the 

 basis of mental activity. How far the mental action is a 

 mere accompaniment of the physical changes, and how 

 far it can react upon them, is a question which cannot be 

 discussed here. But the study of the insane seems to point 

 to the conclusion that the individual does certain things and 

 has certain ideas as concomitant results of faulty brain 

 action, rather than that his actions are a result of the 

 modified ideas. 



2. Time of Cerebral Action The cerebral mechanism 

 takes a very appreciable time to act, and the time varies 

 with the complexity of the action and with the condition 

 of the nervous apparatus. 



Of the time between the presentation of a flash of light to 



