PROTOPLASM AND LIFE. 747 



assert as much as we are justified in doing. Here we stand upon the 

 boundary between life in its proper conception, as a group of phe- 

 nomena having irritability as their common bond, and that other and 

 higher group of phenomena which we designate as consciousness or 

 thought, and which, however intimately connected with those of life, 

 are yet essentially distinct from them. 



When the heart of a recently killed frog is separated from its body 

 and touched with the point of a needle, it begins to beat under the 

 excitation of the stimulus, and we believe ourselves justified in refer- 

 ring the contraction of the cardiac fibers to the irritability of their 

 protoplasm as its proper cause. We see in it a remarkable phenome- 

 non, but one nevertheless in which we can see unmistakable analogies 

 with phenomena purely physical. There is no greater difficulty in 

 conceiving of contractility as a property of protoplasm than there is 

 of conceiving of attraction as a property of the magnet. 



When a thought passes through the mind, it is associated, as we 

 have now abundant reason for believing, with some change in the 

 protoplasm of the cerebral cells. Are we, therefore, justified in re- 

 garding thought as a property of the protoplasm of these cells, in the 

 sense in which we regard muscular contraction as a property of the 

 protoplasm of muscle, or is it really a property residing in something 

 far different, but which may yet need for its manifestation the activity 

 of cerebral protoplasm ? 



If we could see any analogy between thought and any one of the 

 admitted phenomena of matter, we should be justified in accepting the 

 first of these conclusions as the simplest, and as affording an hypothesis 

 most in accordance with the comprehensiveness of natural laws ; but 

 between thought and the physical phenomena of matter there is not 

 only no analogy, but there is no conceivable analogy ; and the obvious 

 and continuous path which we have hitherto followed up in our rea- 

 sonings from the phenomena of lifeless matter through those of living 

 matter here comes suddenly to an end. The chasm between uncon- 

 scious life and thought is deep and impassable, and no transitional 

 phenomena can be found by which as by a bridge we may span it 

 over ; for even from irritability, to which, on a superficial view, con- 

 sciousness may seem related, it is as absolutely distinct as it is from 

 any of the ordinary phenomena of matter. 



It has been argued that because physiological activity must be a 

 property of every living cell, psychical activity must be equally so, 

 and the language of the metaphysician has been carried into biology, 

 and the " cell-soul " spoken of as a conception inseparable from that of 

 life. 



That psychical phenomena, however, characterized as they essen- 

 tially are by consciousness, are not necessarily coextensive with those 

 of life, there can not be a doubt. How far back in the scale of life 

 consciousness may exist we have as yet no means of determining, nor 



