There is a constant succession of books on the subject of comparative grammar, for the use both of students and of the general public; yet it does not seem that we are offered what we really need. Language is full of lessons for those who know how to question it. Through all the centuries humanity has deposited in Language the acquisitions of material and moral life. But it must be approached from the side on which it appeals to the mind. If we limit ourselves to the changes of vowels and consonants, the study is reduced to the proportions of a merely secondary branch of acoustics and physiology; if we think it enough to enumerate the losses undergone *by the machinery of grammar, we give the impression of a building that is falling into ruins; if we confine ourselves to vague theories on the origin of Language, we merely add an unprofitable chapter to the history of systems.