In this, science has made a considerable advance upon common sense in its interpretations of human behavior, but has introduced no new principle; it has simply made its statements more detailed and exact. For example, common sense has observed that "the burnt child shuns the fire," that "the moth seeks the flame." These are both statements of truths of undoubted generality. In order to give them the validity of scientific truth, however, we need to know what there is in the nature of the processes involved that makes it inevitable that the child should shun the fire and the moth should seek the flame. It is not sufficient to say that the action in one case is instinctive and in the other intelligent, unless we are able to give precise and definite meanings to those terms; unless, in short, we are able to point out the precise mechanisms through which these reactions are carried out. The following illustration from Loeb's volume on the comparative physiology of the brain will illustrate the distinction between the common sense and the more precise scientific explanation of the behavior in man and the lower animals. It is a well-known fact that if an ant be removed from a nest and afterward put back it will not be attacked, while almost invariably an ant belonging to another nest will be attacked. It has been customary to use the words memory, enmity, friendship, in describing this fact. Now Bethe made the following experiment: an ant was placed in the liquids (blood and lymph) squeezed out from the bodies of nest companions and was then put back into its nest; it was not attacked. It was then put in the juice taken from the inmates of a "hostile" nest and was at once attacked and killed. Bethe was able to prove by special experiments that these reactions of ants are not learned by experience, but are inherited. The "knowing" of "friend and foe" among ants is thus reduced to different reactions, depending upon the nature of the chemical stimulus and in no way depending upon memory. Here, again, there is no essential difference between the common sense and the scientific explanation of the behavior of the ant except so far as the scientific explanation is more accurate, defining the precise mechanisms by which the recognition of "friend and foe" is effected, and the limitations to which it is subject. Another result of the study of the comparative behavior of man and the lower animals has been to convince students that there is no fundamental difference between what was formerly called intelligent and instinctive behavior; that they may rather be reduced, as has been said, to the elementary form of reaction represented by the simple reflex in animals and the tropism in plants. Thus Loeb says: