SENSATION A PROPERTY OF LIFE 49 



releasing a catch which permits the starting of 

 machinery that is actuated by an instinctive 

 impulse. In the higher animals the ganglia are 

 collected into the spinal cord or the brain ; in 

 the lower they form less complicated systems, 

 sometimes very loosely connected. But we must 

 remember that this elaboration of sense organ, 

 nerve and ganglion is by no means essential. 

 The microscopic protozoa, which are regarded 

 by an evolutionist as his remotest ancestors, 

 possess no organs whatever for sensation. They 

 are simply small masses of nitrogenous jelly, so 

 far as can be ascertained of like texture through- 

 out, except for a small spot where there has been 

 some sort of concentration into a nucleus. Yet 

 all of them are sensitive to light and to touch : 

 some of them can even distinguish blue light from 

 light of other kinds. They can recognize their 

 peculiar food, and certain of them construct the 

 most beautiful little shells, the designing of which 

 by a man would be taken to show much delicacy 

 of conception. Plants are, of course, very sensi- 

 tive to light ; some of them, such as the sensitive 

 mimosa and a species of balsam,|violently resent 

 touch, and two species (Drosera and Dionsea), 

 the leaves of which are able to digest captured 

 insects, exhibit in divergent manners very delicate 

 sensibilities that are of use to them in distinguish- 

 ing flies from other objects. A study of natural 

 history shows us, in fact, that sensation is a pro- 

 perty of life, not a function of any description of 

 organ. 



Did our sensory impressions originate on the 

 exterior surface of our bodies there might be some 

 prima facie ground for the idea that they repre- 

 sent things as they are that there exist, in fact, 



