MENTAL PHYSIOLOGY. 711 



The warning against these experiments, which are too much the pas- 

 time of the idle, the hysterical, and the foolish, is of weighty import : 



" The undue repetition of such experiments, however, and especially their 

 repetition on the same individuals, is to be strongly deprecated ; for the state 

 of mind thus induced is essentiallj a morbid one, and the reiterated suspension 

 of that volitional power over the direction of the thoughts, which is the highest 

 attribute of the human mind, can scarcely do otherwise than tend to its perma- 

 nent impairment" (p. 565). 



The question of " Unconscious Cerebration " or *' Latent Mental 

 Modification," which is peculiarly Dr. Carpenter's own, is too impor- 

 tant and unsettled to be fully discussed within the brief limits of a 

 review. Dr. Carpenter thinks that his views had been anticipated by 

 Sir William Hamilton, but the passage he quotes from that philoso- 

 pher scarcely appears to us to detract from the author's priority of 

 thought. Sir W. Hamilton's "mental activities and passivities of 

 which we are unconscious, but which manifest their existence by 

 effects of which we are conscious," are plainly indicated by the sen- 

 tence which follows as referring to the unknown and the incognizable. 

 We are conscious of the knowable, unconscious of the unknowable. 



" There are many things which we neither know nor can know in them- 

 selves, but which manifest their existence indirectly through the medium of 

 their effects. This is the case with the mental modifications in question. They 

 are not in themselves revealed to consciousness, but as certain feats of con- 

 sciousness ; suppose them to exist, and to exert an influence on the mental pro- 

 cesses, we are thus constrained to admit as modifications of mind what are not 

 phenomena of consciousness " (p. 518). 



Hamilton proceeds to explain that we can only be conscious of a 

 determinate state or mental condition which supposes a transition 

 from some other state : " But as the modification must be present be- 

 fore we have a consciousness of it, we can have no consciousness of 

 its rise or awakening, for this is also the rise or awakening of con- 

 sciousness." 



If all this means any thing, it must mean that we are only con- 

 scious of mental states which exist at the time, and that we are un- 

 conscious of preceding mental states, or of the transition from pre- 

 ceding to existing states. How Dr. Carpenter can hatch unconscious 

 cerebration out of that Qg^ we cannot imagine. 



Neither can we see how John S. Mill can be thought " explicitly 

 to accept the doctrine of unconscious cerebration," seeing that he 

 *' considers unconscious mental modification as a contradiction in 

 terms ; attributing the phenomena to unrecognized changes in the 

 substance of the brain which he regards as the constant physical at- 

 tendants of mental modifications." 



No doubt there are many brain-changes of which we are not con- 

 scious, but mental change, without consciousness, is, according to this 



