The machines, says Cuvier, which are the object of our researches, cannot be demonstrated without being destroyed. We have no means of discovering what would result from the absence of one or several of their parts, and consequently we remain ignorant of the operation of each of these parts in producing the total effect. Fortunately, nature herself seems to have prepared for us the means of supplying that want which arises from the impossibility of making certain experiments on living bodies. The different classes of animals exhibit almost all the possible combinations of organs. We find them united, two and two, three and three, and in all proportions; while at the same time it may be said that there is no organ of which some class or some genus is not deprived. A careful examination of the effects which result from these unions and privations is therefore sufficient to enable us to form probable conclusions respecting the nature and the use of each organ, or form of organ. In the same manner, we may proceed to ascertain the use of the different parts of the same organ, and to discover those which are essential, and separate them from those which are only accessary. It is sufficient to trace the organ through all the classes which possess it, and to examine what parts constantly exist, and what change is produced in the respective functions of that organ, by the absence of those parts which are wanting in certain classes. Thus, says Richerand, the cellular structure of the lungs which cannot be clearly demonstrated in man, on account of the excessive tenuity of their smallest lobuli, evidently displays itself in the vesicular lungs of salamanders and frogs; in the same manner, the scales covering the bodies of fish and reptiles, or the claws of birds, give us a just idea of the structure of the epidermis, and of the disposition of its small laminæ that are laid over each other on a part of their surface, &c. Vegetable life, justly, says the same author, compared in its resources and effects with animal life, would throw very great light on several phenomena, which, at present, it is difficult for us to conceive and to explain. The medical treatment of vegetables, which is almost entirely surgical, would be equally benefited by these researches. Thus the wounds of vegetables, like those of the human body, are much less dangerous when their surface is smooth, than when their edges are rough, lacerated, or contused. Trees cut down with a saw bud with difficulty, whilst those felled with an axe vegetate more briskly.—The saw tears the vegetable structure and produces a greater or less alteration in organization. The unequal surface of a tree thus cut down retains humidity, as destructive to the trunk, of which it induces a rottenness, as too great a quantity of pus, that so habitually moistens the surface of an animal wound, destroys granulation and prevents cicatrization.