254 Heredity. 



' No thought, no feeling,' says the author, ' is ever manifested, 

 save as the result of a physical force. This principle will before 

 long be a scientific common place.' 



"" They who hold this doctrine observe that nervous force, which 

 ultimately results from nutrition, must, after it is produced, be 

 expended in one or other of these three ways : either by acting on 

 the viscera, the heart, or the digestive organs, as is the case in 

 deep emotion; or by acting on the muscles and producing move- 

 ments, gestures, and various expressions of the physiognomy ; or 

 by causing the excitation to pass to some other part of the nervous 

 system, and hence result those successive states which make up 

 consciousness. Sensations excite ideas and emotions ; the latter 

 in turn awaken other ideas and emotions, and so on that is to 

 say, the tension existing in certain nerves, or groups of nerves, 

 when they give us sensations, ideas, or emotions, produces an 

 equivalent tension in some, other nerves, or groups of nerves, with 

 which they are connected. 



But the facts cited in support of this thesis do not appear to us 

 to be all equally conclusive. Some of them are no doubt trans- 

 formations, but then others are rather correspondences. Thus, the 

 pain which is transformed into cries and extravagant contortions is 

 of short duration ; pain which endures is reticent of expression. 

 And the same is to be said of anger. But in certain cases for 

 example, in the cerebral excitation produced by hasheesh or opium 

 it is not quite certain that between the nervous state and the 

 mental state there exists equivalence, transformation, and not 

 simply correspondence. 



This doctrine of the correlation of physical forces and thought 

 is as yet hardly more than an outline. It is still in the qualitative 

 period, and it is doubtful whether it will very soon enter on the 

 quantitative period, which alone can constitute it a science. It is 

 however a promising field, and one well adapted to exercise free 

 and daring minds. If it could be demonstrated scientifically, it is 

 evident that then the problem of the relations between the physical 

 and the moral would come before us in a new aspect : it would be 

 only a particular case of the law of the correlation of forces. We 

 need not say that such a solution, restricted to experience, would 



