Seneca, Epistulae Morales
108.17-22 (tr. Richard M. Gummere):
 Inasmuch as I have begun to explain to you how much greater was my impulse to approach philosophy in my youth than to continue it in my old age, I shall not be ashamed to tell you what ardent zeal Pythagoras inspired in me. Sotion used to tell me why Pythagoras abstained from animal food, and why, in later times, Sextius did also. In each case, the reason was different, but it was in each case a noble reason.
 Sextius believed that man had enough sustenance without resorting to blood, and that a habit of cruelty is formed whenever butchery is practised for pleasure. Moreover, he thought we should curtail the sources of our luxury; he argued that a varied diet was contrary to the laws of health, and was unsuited to our constitutions.
 Pythagoras, on the other hand, held that all beings were interrelated, and that there was a system of exchange between souls which transmigrated from one bodily shape into another. If one may believe him, no soul perishes or ceases from its functions at all, except for a tiny interval -- when it is being poured from one body into another. We may question at what time and after what seasons of change the soul returns to man, when it has wandered through many a dwelling-place; but meantime, he made men fearful of guilt and parricide, since they might be, without knowing it, attacking the soul of a parent and injuring it with knife or with teeth -- if, as is possible, the related spirit be dwelling temporarily in this bit of flesh!
 When Sotion had set forth this doctrine, supplementing it with his own proofs, he would say: "You do not believe that souls are assigned, first to one body and then to another, and that our so-called death is merely a change of abode? You do not believe that in cattle, or in wild beasts, or in creatures of the deep, the soul of him who was once a man may linger? You do not believe that nothing on this earth is annihilated, but only changes its haunts? And that animals also have cycles of progress and, so to speak, an orbit for their souls, no less than the heavenly bodies, which revolve in fixed circuits?
 Great men have put faith in this idea; therefore, while holding to your own view, keep the whole question in abeyance in your mind. If the theory is true, it is a mark of purity to refrain from eating flesh; if it be false, it is economy. And what harm does it do to you to give such credence? I am merely depriving you of food which sustains lions and vultures."
 I was imbued with this teaching, and began to abstain from animal food; at the end of the year the habit was as pleasant as it was easy. I was beginning to feel that my mind was more active; though I would not today positively state whether it really was or not. Do you ask how I came to abandon the practice? It was this way: the days of my youth coincided with the early part of the reign of Tiberius Caesar. Some foreign rites were at that time being inaugurated, and abstinence from certain kinds of animal food was set down as a proof of interest in the strange cult. So at the request of my father, who did not fear gossip, but who detested philosophy, I returned to my previous habits; and it was no very hard matter to induce me to dine more comfortably.
 Quoniam coepi tibi exponere quanto maiore impetu ad philosophiam iuvenis accesserim quam senex pergam, non pudebit fateri quem mihi amorem Pythagoras iniecerit. Sotion dicebat quare ille animalibus abstinuisset, quare postea Sextius. Dissimilis utrique causa erat, sed utrique magnifica.
 Hic homini satis alimentorum citra sanguinem esse credebat et crudelitatis consuetudinem fieri ubi in voluptatem esset adducta laceratio. Adiciebat contrahendam materiam esse luxuriae; colligebat bonae valetudini contraria esse alimenta varia et nostris aliena corporibus.
 At Pythagoras omnium inter omnia cognationem esse dicebat et animorum commercium in alias atque alias formas transeuntium. Nulla, si illi credas, anima interit, ne cessat quidem nisi tempore exiguo, dum in aliud corpus transfunditur. Videbimus per quas temporum vices et quando pererratis pluribus domiciliis in hominem revertatur: interim sceleris hominibus ac parricidii metum fecit, cum possent in parentis animam inscii incurrere et ferro morsuve violare, si in quo cognatus aliqui spiritus hospitaretur.
 Haec cum exposuisset Sotion et implesset argumentis suis, 'non credis' inquit 'animas in alia corpora atque alia discribi et migrationem esse quod dicimus mortem? Non credis in his pecudibus ferisve aut aqua mersis illum quondam hominis animum morari? Non credis nihil perire in hoc mundo, sed mutare regionem? nectantum caelestia per certos circuitus verti, sed animalia quoque per vices ire et animos per orbem agi? Magni ista crediderunt viri.
 Itaque iudicium quidem tuum sustine, ceterum omnia tibi in integro serva. Si vera sunt ista, abstinuisse animalibus innocentia est; si falsa, frugalitas est. Quod istic credulitatis tuae damnum est? alimenta tibi leonum et vulturum eripio.'
 His ego instinctus abstinere animalibus coepi, et anno peracto non tantum facilis erat mihi consuetudo sed dulcis. Agitatiorem mihi animumesse credebam nec tibi hodie adfirmaverim an fuerit. Quaeris quomodo desierim? In primum Tiberii Caesaris principatum iuventae tempus inciderat: alienigenatum sacra movebantur et inter argumenta superstitionis ponebatur quorundam animalium abstinentia. Patre itaque meo rogante, qui non calumniam timebat sed philosophiam oderat, ad pristinam consuetudinem redii; nec difficulter mihi ut inciperem melius cenare persuasit.