One day the prisoner ordered his gaoler to buy him a particular book, and Laurent, objecting to an expense which seemed to him quite needless, offered to borrow him a book of one of the other prisoners, in exchange for one of his own. Here at last was an opportunity. Casanova chose a volume out of his small library, and gave it to the gaoler, who returned in a few minutes with a Latin book belonging to one of the other prisoners. Pen and ink were forbidden, but in this book Casanova found a fragment of paper; and he contrived, with the nail of his little finger, dipped in mulberry juice, to write on it a list of his library--and returned the volume, asking for a second. The second came, and in it a short letter in Latin. The correspondence between the prisoners had really begun. The writer of the Latin letter was the monk Balbi, imprisoned in the Leads with a companion, Count Andre Asquin. He followed it by a much longer one, giving the history of his own life, and all that he knew of his fellow-prisoners. Casanova formed a very poor opinion of Father Balbi's character from his letters; but assistance of some kind he must have, since the gaoler must needs discover any attempt to break through the ceiling, unless that attempt was made from above. But Casanova soon thought of a plan by which Balbi could break through _his_ ceiling, undiscovered. 'I wrote to him,' he relates, 'that I would find some means of sending him an instrument with which he could break through the roof of his cell, and having climbed upon it, go to the wall separating his roof from mine. Breaking through that, he would find himself on _my_ roof, which also must be broken through. That done, I would leave my cell, and he, the Count, and I together, would manage to raise one of the great leaden squares that formed the highest palace roof. Once outside _that_, I would be answerable for the rest. 'But first he must tell the gaoler to buy him forty or fifty pictures of saints, and by way of proving his piety, he must cover his walls and ceiling with these, putting the largest on the ceiling. When he had done this, I would tell him more. 'I next ordered Laurent to buy me the new folio Bible that was just printed; for I fancied its great size might enable me to conceal my tool there, and so send it to the monk. But when I saw it, I became gloomy--the bolt was two inches longer than the Bible. The monk wrote to me that the cell was already covered according to my direction, and hoped I would lend him the great Bible which Laurent told him I had bought. But I replied that for three or four days I needed it myself.