interference. Such a universal and absolute break-down is unknown to nature. 6. All this appears most clearly in organic beings, plants and animals. Organisms, except the very lowest, are compounds of a number of different parts, each fulfilling a special function for the good of the whole. There is no idle constituent in an organic body, none without its function. What are called _rudimentary_ organs, even if they serve no purpose in the individual, have their use in the species, or in some higher genus. In the animal there is no idle natural craving, or appetite. True, in the individual, whether plant or animal, there are many potentialities frustrate and made void. That is neither here nor there in philosophy. Philosophy deals not with individuals but with species, not with Bucephalus or Alexander, but with _horse_, _man_. It is nothing to philosophy that of a thousand seeds there germinate perhaps not ten. Enough that one seed ever germinates, and that all normal specimens are apt to do the like, meeting with proper environment. That alone shows that seed is not an idle product in this or that class of living beings. 7. But, it will be said, not everything contained in an organism ministers to its good. There is refuse material, only good to get rid of: there are morbid growths; there is that tendency to decay, by which sooner or later the organism will perish. First, then, a word on diseases. Diseases are the diseases of the individual; not of the race. The race, as such, and that is what the philosopher studies, is healthy: all that can be imputed to the race is liability to disease. That liability, and the tendency to decay and die, are found in living things, because their essence is of finite perfection; there cannot be a plant or animal, that has not these drawbacks in itself, as such. They represent, not the work of nature, but the failure of nature, and the point beyond which nature can no further go. 8. On the preceding observations Aristotle formulated the great maxim--called by Dr. Thomas Browne, _Religio Medici_, p. i., sect. 15, "the only indisputable axiom in philosophy,"--_Nature does nothing in vain_. (Ar., _Pol._, I., viii., 12; _De Anima_, III., ix., 6; _De part. animal._, I. i., p. 641, ed. Bekker.)