No greater mistake can be made than to imagine that what has been written latest is always the more correct; that what is written later on is an improvement on what was written previously; and that every change means progress. Men who think and have correct judgment, and people who treat their subject earnestly, are all exceptions only. Vermin is the rule everywhere in the world: it is always at hand and busily engaged in trying to improve in its own way upon the mature deliberations of the thinkers. So that if a man wishes to improve himself in any subject he must guard against immediately seizing the newest books written upon it, in the assumption that science is always advancing and that the older books have been made use of in the compiling of the new. They have, it is true, been used; but how? The writer often does not thoroughly understand the old books; he will, at the same time, not use their exact words, so that the result is he spoils and bungles what has been said in a much better and clearer way by the old writers; since they wrote from their own lively knowledge of the subject. He often leaves out the best things they have written, their most striking elucidations of the matter, their happiest remarks, because he does not recognise their value or feel how pregnant they are. It is only what is stupid and shallow that appeals to him. An old and excellent book is frequently shelved for new and bad ones; which, written for the sake of money, wear a pretentious air and are much eulogised by the authors’ friends. In science, a man who wishes to distinguish himself brings something new to market; this frequently consists in his denouncing some principle that has been previously held as correct, so that he may establish a wrong one of his own. Sometimes his attempt is successful for a short time, when a return is made to the old and correct doctrine. These innovators are serious about nothing else in the world than their own priceless person, and it is this that they wish to make its mark. They bring this quickly about by beginning a paradox; the sterility of their own heads suggests their taking the path of negation; and truths that have long been recognised are now denied—for instance, the vital power, the sympathetic nervous system,generatio equivoca, Bichat’s distinction between the working of the passions and the working of intelligence, or they return to crass atomism, etc., etc. Hence the course of science is often retrogressive.