THE SENSE OF TOUCH 481 



holds that these reactions are simply the results of physical 

 or chemical changes produced in the protoplasm by the 

 stimuli, and that the movement toward food, and away 

 from particles which are not food, can be fully explained by 

 the laws of physics or chemistry, and no more indicate con- 

 sciousness than movements of iron particles to a magnet 

 prove consciousness in the particles. 



The latter school has conducted exhaustive experiments 

 to demonstrate its point and has proved pretty conclu- 

 sively that many of these responses to stimuli on the part of 

 protozoans are the resiilt of the chemical or physical action 

 of the stimulus upon the protoplasm. Thus the move- 

 ment of an amceba toward a food particle they explain as 

 due to chemical attraction between the compounds in the 

 protoplasm and the food, and not to conscious choice of the 

 amoeba. Recent investigations (notably those of Professor 

 Jennings of the University of Pennsylvania) have shown 

 responses that are difficult to explain by these natural 

 laws and the question is still unsettled. 



At any rate, these reactions to stimuli result in move- 

 ments beneficial to the organism, and hence, whether they 

 be indications of consciousness or not, they correspond to 

 the function of sensation in higher forms. 



Development op the Sensory Organs. 



The sense of touch. — This sense is found in all ani- 

 mal forms. In the ccslenterates it is confined to a few 

 sensory cells which are located in special regions of the 

 body. In forms higher than the ccelenterates it is pretty 

 generally distributed over the whole body covering, though 

 some parts are more sensitive than others. In every case 



BDDT. PHTS. — 31 



