968 Dynamic Theory. 



into heat. Thus, it is a term in a series of molecular physical move- 

 ments, and is therefore itself a form of ph}-sical motion. 



As observed above, our consciousness consists of separate sensations, 

 each of which relates to a definite nervous action that preceded it. We 

 have a sensation of an impression of the impact from a luminous body, 

 another of a perception of what the body is, another of an idea of the 

 cause of it being luminous, &c. Thus, the sensation is always in asso- 

 ciation with, and subsequent to, another mental act; and when it is 

 called tip in recollection, the recollection of its related mental act is apt 

 to be called up too. This is more especially the case with objective sen- 

 sations in their relation to their ideas and perceptions, the sensation of 

 the idea and the idea itself, often appearing to us identical. But also 

 in the case of subjective sensations, such as the feeling of hunger and 

 plethora, sea-sickness, giddiness, feebleness, and the like, we ordinarily 

 fail to disconnect the sensation from the nervous action which precedes 

 it; but in this case the sensation alone is recollected, while the antece- 

 dent action is obscured, as a rule, although it may be brought out again 

 in rare cases, as when a person becomes nauseated from the revival of a 

 memory of excessive disgust. This would be a case of reverse action 

 in the nervous machinery, such as we have observed in relation to illu- 

 sions, &c. The back action of the nervous machine in the production 

 of the nausea, reverses the action of the muscles concerned in swallow- 

 ing, if carried to an extreme. ( See page 611.) 



There is no difference in principle between subjective and objective 

 reactions. To the organs of sensation in the brain, all other ganglia 

 and nervous machinery are objective, regardless of whether they are 

 close by them in the cerebrum, or down in the medulla oblongata, or 

 even in the great ganglions and plexuses of the sympathetic system 

 among the viscera. 



The distinction which thus shows itself between the sensations on one 

 side, and the impressions and other nervous actions on the other side, 

 indicates that their functions are separate, and carried on in separate 

 organs ; and that the former, although consequent upon the latter, are 

 not merely subdivisions or incidents of them. We thus conclude sen- 

 sations to be motions of matter, thus distinguishing that they are not 

 properties of matter, for a property is a constant and stolid condition 

 of a body, which remains until the environment changes the body it- 

 self. For example, a piece of spring-steel of a particular shape, pos- 

 sesses a property of elasticity, which, when the spring is snapped, 

 causes it to vibrate for a time, until friction gradually changes the mo- 

 tion to heat. Elasticity is its property, vibration its function. The 

 function of sensation comes upon stimulation, and goes as its activit}^ 

 is dissipated into heat, or communicates activity to other nervous ele- 



