The various forms of protein which are found constituting the muscles, tissues, and solid matters of the blood of animals, are thus evi dently derived from the vegetable kingdom ; that silent but ever active laboratory in which so much of the chemical economy of nature is carried on. From the gaseous matters of the atmosphere, more especially carbonic acid, ammonia, and watery vapour, the org-anic ele ments, carbon, oxygen, hydrogen, and nitrogen, are derived ; and from the various saline ingredients of the soil, those inorganic sub stances which are essential to the growth and well-being of mankind and of the lower ani mals are readily abstracted by the absorbent fibres of the roots. Thus formed, plants con stitute the source from which all living beings obtain the nourishment which is necessary to their existence, and of which the very sub stance of their bodies is composed ; an arrange ment which is most strikingly evident in the herbivora, because vegetables are their only food, but not less certainly in the carnivora, since the animal flesh which they consume is either that of the herbivora or of some ani mals which have fed upon thern.
It is impossible not to admire the simplicity which pervades the whole of this vast scheme, in which we find so large a portion of the animal body composed of materials almost identical in composition, though differing so essentially in their use and applications. If one of these principles, albumen or casein for instance, be contained in the food in quantity insufficient for the requirements of the animal, it is readily supplied from one of the others by the addition or removal of a minute quantity of sulphur or phosphorus, both of which are always present ; whereas, if this beautiful pro vision had not been made, a large amount of disease and suffering would have almost neces sarily ensued. Moreover, had the task of ela borating these highly complex principles from more simple ingredients devolved on ani mals themselves, much complicated machinery would probably have been required, which would have added unnecessarily to the com plexity of the body, and consequently to the sources of physical derangement.