1002 Dynamic Theory. 



vironment outside of the body, that is, the objective sensations. It 

 might be rash to assume that the simplest animal that eats does so from 

 the stimulation of an unpleasant sense of " goneness. " But we know 

 we do so ourselves, and when we observe the other mammals eat, they 

 exhibit every indication of being actuated by the same motive. They 

 appear to endure the pains of hunger, and enjoy the comfortable sense 

 of satiety. As we descend the animal scale, we find the fishes eagerly 

 pursuing their prey, or cunningly lying in wait for it, undoubtedly ani- 

 mated by a similar impulse, thus exhibiting not only sensibility, .but 

 foresight, imagination, and reason. The higher genera among the mol- 

 lusks, such as the octopus, express themselves in their actions as the 

 .fishes do. If we go lower the actions become less demonstrative, but 

 with the lowest, the stomach, or body cavity, is a hung^ receptacle for 

 whatever food comes in its way, and a center from which come im- 

 pulses to set in motion whatever machinery of limbs the animal pos- 

 sesses, for the apparent purpose of keeping this receptacle supplied. 

 The physiological basis of the sensation of hunger is without doubt the 

 unsaturated chemism of the elements that compose the tissues of the 

 wearing parts of the body. This physiological basis exists in every 

 animal from the amosba up to man. In the former, and in other simple 

 animals, this unsatisfied chemism is perhaps all the force there is for the 

 acquirement of food. An amo3ba, a sponge, or a rhizopod to which 

 a supply of food is simply a lucky accident, and which therefore does 

 not make an effort, absorbs its food probably without sensibility or pre- 

 vious sensation of hunger. But somewhere in the scale of life, and not 

 very far above the lowest, the sense of hunger does accompan} r the un- 

 satisfied chemical state of the tissues. It is superadded to it and ap- 

 pears somehow to grow out of it, or at any rate it is developed in rela- 

 tion to it, and in all animals that are active in pursuit of food it be- 

 comes the chief incentive to exertion. The pleasurable and painful 

 sensations which arise in connection with the animal or outer part of 

 the body, such as those due to temperature, pressure, contusion, &c. f 

 are of later development; while those relating to companionship, care for 

 the young, and the emotions, anger, attachment, rage, fear, &c. , are still 

 later. There is a gradual development of sensibility in relation to more 

 and more of the animal activities as we ascend the scale, the sensibility 

 without doubt following close upon the development of the activity. 



We may divide subjective sensations into two general classes, which 

 may be styled the positive and the negative; for it is apparent upon re- 

 flection that the state of the tissues in which the chemism is unsaturated, 

 has its antithesis in a condition in which it is satisfied and in which any 

 further stimulation produces repulsion instead of attraction, that is, 

 nausea or disgust instead of hunger. While hunger is probably the 



