In the process of deglutition, or swallowing the nourishment essential to the existence of all the more perfect animals,--since the food and the air for respiration pass for a time through a common opening, the pharynx,--it is extremely important that the passage to the lungs should be most vigilantly guarded; since strangulation would follow the introduction there of any thing but air. Accordingly, the entrance of the glottis is so sensitive, that the approach of the food causes it to close. But lest this security should sometimes fail, we have an additional guard in the epiglottis, which shuts down like a valve upon the orifice. Even with this double precaution, strangulation sometimes follows the act of deglutition. How much oftener would it occur, had not benevolence thus multiplied its vigilant sentinels at the point of danger! Another illustration of this argument lies in the fact, that many of the organs of animals and plants possess the power, when an exigency requires it, of greatly increasing their action. When, for instance, an unusual quantity of osseous matter is requisite to repair a broken bone, the glands, whose office it is to elaborate that matter, are capable of secreting an extraordinary quantity, until the injury is repaired. Of an analogous character is the sympathy existing between the different organs, so that when one has an unusual amount of labor to perform, the rest impart of their nervous energy to sustain their overtasked companion. Thus, and thus only, could animals be carried through many of the severe exigencies of their existence. Their organs help one another, just as if they were conscious of one another's necessities, and were prompted by benevolence to aid the weakest. In like manner, some of the organs possess the power of vicarious secretion; that is, of producing, in peculiar circumstances, secretions that are usually made by other glands. How they can do this, and how they can know when to do it, are among the mysteries of physiology. Nevertheless, the object of this arrangement is most obvious, viz., the continuance of health and life in spite of accidents, which would otherwise prove fatal. The same vicarious system is manifest in the well-known examples, where the loss of one or more of the senses gives increased acuteness to the rest. The sense of touch, for instance, in the blind man, has sometimes proved no mean substitute for eyes; and, indeed, any of the senses by cultivation, in peculiar exigencies, may be prodigiously strengthened.