210 



This, and many other equally satisfactory observations, appear to lay so 

 good a foundation for a proper appreciation of the scope of sensibility that 

 we are surprised and disheartened to find him finally in a hopeless muddle 

 of plants, monads and molecules, and when he has affirmed that " sensi- 

 bility stands for the objective phenomena exhibited by an organism under 

 stimulation," he must needs add, to save himself from possible entangle- 

 ment, "or, more definitely, for the reaction of a neuromuscular mechan- 

 ism." No great progress can be hoped for in the study of nerveless 

 organisms by a constant comparison of their behavior with that of organisms 

 with nerves and nerve centers. There is need of a different method. 



This review of the present state of knowledge regarding the relations of 

 sensibility in plants and animals shows an astonishing absence of agree- 

 ment and a total lack of a rational basis. The confusion, it seems to me, 

 is due to a disregard of the conditions under which sensibility has been de- 

 veloped in the two divisions of the organic world. Knowing that irrita- 

 bility is a fundamental property of all living matter, let us ask ourselves 

 what advantages the animal or plant could secure by its special develop- 

 ment. That is, given this universal property of organisms, how could it be 

 developed into special senses ? It is unquestionable that the paramount 

 necessity of the organism is self-preservation. To secure food, to keep out 

 of harm's way , to obtain the proper supply of air, moisture and heat, may be 

 considered the fundamental necessities of every organism, whether man or 

 monad, tree or microbe. Considering for the present only the higher 

 organisms, we note that, if an animal desires food, its sight and scent aid 

 in searching for it, if in danger its sight and hearing enable it to escape, 

 when food is obtained taste and smell indicate whether it is to be eaten or 

 rejected, while touch gives a variety of sensations relating to food, bodily 

 comfort and protection. Our present purpose does not require any men- 

 tion of intellectual sensations. All the lower animals, down to the simplest 

 unicellular forms, "the little lumps of protoplasm" described by Heeckel, 

 possess one or more of these senses, and some animals may possibly possess 

 other kinds in addition. The point to be especially noted here is that each 

 individual animal (with a few exceptions among the lowest forms) has the 

 power to flee when its senses indicate danger, or to advance when desirous 

 of food, or to seek another place if the present one is too wet or too dry, 

 too hot or too cold. 



Let us examine plants in a parallel way. If they need food do they have 

 sight and scent to aid them in searching for it ? No, because they are 



