NERVOUS FORCE AND WORK. 931 



the solid constituents of all of which, in a Man weighing 150 Ibs., 

 would be upwards of 8 oz. per diem. Playfair supposes that, whilst 

 most of the substances are reabsorbed, a certain portion of each under- 

 goes chemical change, being, as it were, degraded, and becoming unfit 

 for entering the circulation. This remains, therefore, as a quantita- 

 tive expression of the force which has been employed in the processes 

 of primary assimilation. It may be a residual index of such actions, 

 but not a source of power itself, for it escapes unoxidized. All nutri- 

 tive work, implying solidification of material, likewise ultimately passes 

 into heat. 



Electrical Work. 



The currents of electricity developed in the body generally, those 

 found between the arterial and venous blood, in muscle and in nerve, 

 in secreting and in special electric organs, are developed through 

 chemical action, involving waste by oxidation of the blood or tissues, 

 and indirectly therefore of the food, whether of the nitrogenous or non- 

 nitrogenous food, or of both is not yet determined. They do not ap- 

 pear to be derived from friction, changes of temperature, or magnetism, 

 as in the inorganic world. The chemical energy of the body, thus 

 diverted to electric work, cannot, however, be expressed in numbers. 

 Unless it passes off to surrounding objects or media, it is converted 

 into heat, or into motion and heat, within the frame, and so assists in 

 the calorific work. 



Nervous Force and Work. 



As elsewhere mentioned (p. 227), there exists in nervous substance 

 a peculiar electro-polar condition of the nervous molecules, which is 

 altered, not merely by th'e passage of an ordinary electric current 

 through a whole nerve, as is the case with the muscular current, but 

 also when that current, or any other stimulus, traverses a small por- 

 tion of the nerve. The existence of nervous substance is essential to 

 the manifestation of this peculiar condition; the force concerned in its 

 production may be itself what is called the nerve-force, or it may be trans- 

 formed into that force, serving in either case, to excite the contraction 

 of a muscle, on the one hand, or the reflex or sensitive excitability of a 

 nervous centre, on the other. The reaction of a reflex nervous centre 

 may also require, or depend upon, such molecular polarity. Even 

 sensation, and the higher and purely mental processes, are associated 

 with, and rest upon, similar molecular conditions and properties. The 

 special condition of the nervous matter which accompanies sensation, 

 emotion, thought, consciousness, and will, is unknown to us; but the 

 molecular polarity of the nerve-substance is, as much as the nervous 

 substance itself, a part of the constitution of the living animal body. 

 The polar condition of the nervous molecules represents a portion of 

 the vito-physical work of the system ; and variations in it are asso- 

 ciated with changes in the nervous matter itself. These changes are 

 chemical, and imply waste, oxidation, and renovation. All nervous 

 action, or work, requires both food and air, containing stores of force, 



