Water, therefore, which is transparent, colorless, inodorous, and tasteless, is called good and pure, and none other can be called such ; though some medical writers are of opinion, that it is not necessary it should be in this pure state for common use. Such opinion however is undoubtedly erroneous II. In the organized kingdom. Water enters largely into the composition of

organic substances. It constitutes, at least, four fifths of the weight of the animal tissues, being the source of their physical properties, extensibility and flexibility •

This water is not chemically combined in them : for it is gradually given off by

evaporation, and can be extracted at once by strong pressure between blotting-paper.

When deprived of its water, animal matter becomes wholly insusceptible of vitality ;

except in the case of some of the lower animals, which, as well as some plants, revive when again moistened. According to Chevreul, pure water alone can reduce organized substances to this state of softness ; although salt water, alcohol, ether, and oil, are also imbibed by dry animal textures. Moist animal tissues, by virtue of their porosity, allow soluble matters, which come into contact with them, to be

dissolved by the water which they contain, and which oils their pores : if the matters are already in solution, they are imparted by their solutions to the water of the

tissues. Gaseous substances are taken up in the same way. Water exists in nearly as large a proportion in vegetable as in animal substances.