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THE AMERICAN NATURALIST [Vol. XLII 



complicated actions of the individual performed with the 

 aid of this reflex mechanism and without the aid of con- 

 sciousness. He recognizes that a large proportion, if 

 not the majority, of the individual's actions are reflex 

 and unconscious actions. Lastly, he finds in reflex 

 mechanisms no mysterious principle, but an ensemble of 

 the same physico-chemical phenomena, which in one form 

 or another he finds in other than nervous tissues, and in 

 which the principle of the conservation of energy holds 

 good. Turning now to conscious actions, he sees how 

 indispensable to them, at least in the higher animal 

 species and man, is a certain part of the cerebrum, 

 especially the outer layer or cortex; and how the degree 

 of intellectual development varies with the extent and 

 complexity of this material structure. He sees how in- 

 jury or disease of this part, or anything interfering with 

 its proper activity, changes the individual from a sen- 

 tient being into a non-thinking reflex machine. He sees 

 acts, once consciously performed, now relegated to the 

 unconscious reflex sphere. He sees how consciousness 

 disappears in sleep, and how its manifestations vary 

 under the influence of drugs. The cerebral cortex is 

 composed of numberless neurones and is connected by 

 afferent and efferent paths with the other portions of 

 the nervous system. With these facts in mind, and 

 though recognizing the intricacies of mental phenomena, 

 the physiologist gets into the way of thinking that after 

 all the mechanism of cortical actions is really the same 

 as that of other nervous phenomena. He sees no ob- 

 jective, a priori reason why an entirely new causative 

 principle should be introduced to explain the action of 

 this small fraction of the nervous system. Whatever its 

 nature, consciousness appears to him, not as a distinct 

 entity grafted on to certain nerve structures, but as 

 merely one of the modes of manifestation of the activity 

 of those structures, just as chemical, thermal and elec- 

 trical phenomena are other modes. Being thus one of the 

 signs of nervous activity, the physiologist finds it difficult 



