convincing demonstration by dissection concerning respiration and the voice, Boëthus asked him for commentaries on the subject and sent for stenographers.[584] Although Galen in his travels often purchased and carried home with him large quantities of drugs, when he made his first trip to Rome he left all his books in Asia.[585] [Sidenote: Falsification and mistakes in manuscripts.] Galen dates the falsification of title pages and contents of books back to the time when kings Ptolemy of Egypt and Attalus of Pergamum were bidding against each other for volumes for their respective libraries.[586] Works were often interpolated then in order to make them larger and so bring a better price. Galen speaks more than once of the deplorable ease with which numbers, signs, and other abbreviations are altered in manuscripts.[587] A single stroke of the pen or slight erasure will completely change the meaning of a medical prescription. He thinks that such alterations are sometimes malicious and not mere mistakes. So common were they that Menecrates composed a medical work written out entirely in complete words and entitled _Autocrator Hologrammatos_ because it was also dedicated to the emperor. Another writer, Damocrates, from whom Galen often quotes long passages, composed his book of medicaments in metrical form so that there might be no mistake made even in complete words. [Sidenote: Galen as a historical source.] Galen’s works contain occasional historical information concerning many other matters than books and drugs. Clinton in his _Fasti Romani_ made much use of Galen for the chronology of the period in which he lived. His allusions to several of the emperors with whom he had personal relations are valuable bits of source-material. Trajan was, of course, before his time, but he testifies to the great improvement of the roads in Italy which that emperor had effected.[588] Galen sheds a little light on the vexed question of the population of the empire, if Pergamum is the place he refers to in his estimate of forty thousand citizens or one hundred and twenty thousand inhabitants, including women and slaves but perhaps not children.[589] [Sidenote: Ancient slavery.]