932 SPECIAL PHYSIOLOGY. 



which, exhibiting itself first in chemical combination, is transformed 

 into the electro-polarity proper to, and manifested only by the nervous 

 substance built up within the bodies of animals, and capable of being 

 excited by appropriate stimuli. 



The portion of nervous work, performed in the control of the various 

 muscular acts, voluntary or involuntary, and belonging to the animal 

 or vegetative functions, cannot, at present, be dissociated, in any cal- 

 culations, from the muscular work itself. As to the nervous work 

 connected with sensation and other psychical actions and reactions 

 unaccompanied by motor results, it is impossible, at present, to measure 

 them, and Haughton's allotment of the so-called mental work of the 

 body, to a certain proportion of the urea, is purely conjectural. It is 

 not even known how far it may be due to changes in nitrogenous or non- 

 nitrogenous matter; it probably depends upon both. Possibly some es- 

 timate of its amount might be made, by studying the amount and the 

 source of the phosphates formed in the system. Urea is probably pro- 

 duced by the decomposition of nervous substance, especially of the albu- 

 minoid axial fibres, and non-medullated terminal portions of the motor 

 nerves ; urea has been found in the muscles of certain Fishes. The phos- 

 phates of the juice of muscle, and the phosphorus in the red corpuscles of 

 the blood, may be a source of phosphates in the urine; but the cerebric 

 acid of the gray nervous substance is especially characterized by con- 

 taining phosphorus, probably unoxidized; and over-activity and dis- 

 ease of the nervous system, are said to increase the amount of phos- 

 phates so excreted. The oxidation of phosphorus, or of phosphuretted 

 fat, may be one source of electro-polar nerve-force. In any case, such 

 molecular polarity is ultimately transformed into heat within the body, 

 and affords another example of the economy with which the various 

 forms of vito-physical force engendered in the animal system, are em- 

 ployed within it. The energy of every substance oxidized in the body, 

 into whatever form of force it may be transmuted, is doubtless applied 

 with the least possible loss. 



In conclusion, it may be observed, that, although the results of the 

 application of the principles of physical research to the explanation 

 of the physiological phenomena discussed in this Section, are at pres- 

 ent incomplete, yet, considering the extreme complexity of the phe- 

 nomena exhibited by living animals, and the difficulty, even in regard 

 to Man alone, of obtaining correct average numerical data, enough has 

 been determined to render it certain, that all the strictly physical pro- 

 cesses within the body, whether chemical, mechanical, thermic, elec- 

 tric, or photic, are performed by modifications of the common force 

 which produces similar phenomena in the inorganic world around us. 



There exists, however, in the living animal, as in the living vege- 

 table organism, a special formative or organizing energy, evolving the 

 perfect animal or plant from the primitive ovum or ovule, developing 

 its various tissues and organs, and conserving these from the com- 

 mencement to the termination of its individual existence. The in- 

 fluence of this force, moreover, extends from the parent to the off- 

 spring, generation after generation. Its relations to the vito-physical 



