TRANSFORMATION AND EQUIVALENCE OF FORCES. 225 



Excessive activity of mind is habitually accompanied by the 

 excretion of an unusual quantity of the alkaline phosphates. 

 Conditions of abnormal nervous excitement bring on analo- 

 gous effects. And the " peculiar odour of the insane/' im- 

 plying as it does morbid products in the perspiration, shows 

 a connexion between insanity and a special composition of 

 the circulating fluids — a composition which, whether re- 

 garded as cause or consequence, equally implies correlation 

 of the mental and the physical forces. Lastly we 



have to note that this correlation too, is, so far as we can trace 

 it, quantitative. Provided the conditions to nervous action 

 are not infringed on, and the concomitants are the same, 

 there is a tolerably constant ratio between the amounts of 

 the antecedents and consequents. Within the implied lim- 

 its, nervous stimulants and anaesthetics produce effects on 

 the thoughts and feelings, proportionate to the quantities 

 administered. And conversely, where the thoughts and 

 feelings form the initial term of the relation, the degree of 

 reaction on the bodily energies is great, in proportion as they 

 are great: reaching in extreme cases a total prostration of 

 physique. 



Various classes of facts thus unite to prove that the law 

 of metamorphosis, which holds among the physical forces, 

 holds equally between them and the mental forces. Those 

 modes of the Unknowable which we call motion, heat, light, 

 chemical affinity, &c, are alike transformable into each 

 other, and into those modes of the Unknowable which we 

 distinguish as sensation, emotion, thought: these, in their 

 turns, being directly or indirectly re-transformable into 

 the original shapes. That no idea or feeling arises, save 

 as a result of some physical force expended in producing 

 it, is fast becoming a common place of science ; and whoever 

 duly weighs the evidence will see, that nothing but an over- 

 whelming bias in favour of a pre-conceived theory, can ex- 

 plain its non-acceptance. How this metamorphosis 

 takes place — how a force existing as motion, heat, or light, 



