Of all the instincts, two groups or classes stand out from the rest: the responses to organic needs, and the responses to other persons. The first class includes eating, avoiding injury, and many others; the second class includes the herd instinct, the mating instinct and the parental instinct, these three and perhaps no others. {139} These two groups out, the rest are rather a miscellaneous collection, including the "random" or playful activity of young children, locomotion, vocalization, laughter, curiosity, rivalry and fighting. They might be named the "non-specific instincts", because the stimulus for each is not easy to specify, being sometimes another person, so that this group has great social importance, but sometimes being impersonal. This third class might also be called the "play instincts", since they are less essential than the other classes for maintaining the individual life or for propagating the species; and are, we may say, less concerned with the struggle for existence than with the joy of living. Our classification then has three heads: (1) Responses to organic needs, (2) Responses to other persons, (3) Play responses. Responses to Organic Needs Something has already been said [Footnote: See above, pp. 79-81, 112.] of the manner in which an organic state, such as lack of water, acting on internal sensory nerves, arouses in the nerve centers an adjustment towards an end-result, and how, if the end-result cannot immediately be attained, preparatory reactions occur, the preparatory reactions being in some cases closely attached, by nature, to the main tendency, and in other cases only loosely attached so that the tendency leads to trial and error behavior. The reactions that are nearest to the end-result are likely to be closely attached to the main tendency, while those that are farther from the end-result are loosely attached. Thus, in the case of _thirst_, the drinking movement itself is about all, in man, that is purely instinctive, {140} and the way of getting water to the mouth, or the mouth to the water, is a matter for trial and error, and only becomes fixed as the result of a process of learning. Still less can we mention any specific water-seeking reactions, in the human being, that are provided by the native constitution. Yet the whole business of relieving thirst is directed by the native thirst-impulse, and to that extent is an instinctive activity. And shall we say that so simple a matter as meeting this organic need is below the dignity of psychology, and can have little influence on the behavior of mankind? Hardly, when we think of the rôle played by springs, wells and drinking places of all kinds in the life of the race, of aqueducts and reservoirs, of all the beverages that have been invented, and of all the people whose job it has been to provide and dispense them. To be sure, any beverage with a taste, or a "kick", is not simply a thirst-reliever, but makes some