286 THE SCIENCE OF LIFE. 



ing upon the common sensation. What Dr. Carpenter 

 terms " consensual actions " may also originate here, as 

 well as from sensation proper. In this term that emi- 

 nent physiologist includes "all the purely instinctive ac- 

 tions of the lower animals, which make up, with the u re- 

 flex," nearly all the animal functions in many tribes, and 

 which are peculiarly elaborate in their character and 

 wonderful in their results in Insects. Such automatic 

 and involuntary actions as vomiting excited by the sight 

 of a loathsome object, a bad smell, or a disagreeable 

 taste, or laughter excited by tickling, are also classed 

 under this term. 



8. Sensation, or special sense, is caused by an impres- 

 sion on certain parts of the nervous system, which are 

 hence called sensitive. For sensation two things are 

 necessary: an impressible state of the sensitive organs, 

 and a perception by the mind. 



9. Perception is the evidence we have of external ob- 

 jects by means of the senses. It is necessary that the 

 organs and nerves be sound, or false perceptions will re- 

 sult. Ringing noises in the ears, floating specks before 

 the eyes, and many spectral illusions, have their origin 

 in a diseased condition of the organs. Yet that percep- 

 tion is an attribute of mind is evident from the fact that 

 attention is required. The senses may be impressed by 

 their appropriate objects, but without attention they are 

 not perceived. 



10. Memory implies a former conscious experience, 

 either of a physical or mental kind ; its retention, revival, 

 and recognition. The laws of memory, as they are called, 

 or circumstances which excite recollection, have been 



