Philo – Tenth Plague: Death of the Firstborn
Death of the Firstborn (Exodus 11:1–7)
 And Moses said, Thus saith the LORD, About midnight will I go out into the midst of Egypt:
 And all the firstborn in the land of Egypt shall die, from the firstborn of Pharaoh that sitteth upon his throne, even unto the firstborn of the maidservant that is behind the mill; and all the firstborn of beasts.
 And there shall be a great cry throughout all the land of Egypt, such as there was none like it, nor shall be like it any more.
 But against any of the children of Israel shall not a dog move his tongue, against man or beast: that ye may know how that the LORD doth put a difference between the Egyptians and Israel.
Philo, On Dreams (De Somniis) 2.266–2.267
(2.266) And if you see the genuine offspring and the firstborn of Egypt destroyed, namely desire, and pleasures, and pain, and fear, and iniquity, and mirth [Note: aphraino; to be foolish, senseless], and intemperance, and all the other qualities which are similar and akin to these, then marvel and be silent, dreading the terrible power of God;
(2.267) for, say the scriptures, “Not a dog shall move his tongue, nor shall anything, man or beast, utter a sound” [Ex 11:7]; which is equivalent to saying, It does not become either the impudent tongue to bark and curse – nor the man that is within us, that is to say, our dominant mind; nor the cattle-like beast which is within us, that is to say, the outward sense – to boast, when all the evil that was in us has been utterly destroyed, and when an ally from without comes of his own accord to hold his shield over us.
Death of the Firstborn (Exodus 12:29–33)
 And it came to pass, that at midnight the LORD smote all the firstborn in the land of Egypt, from the firstborn of Pharaoh that sat on his throne unto the firstborn of the captive that was in the dungeon; and all the firstborn of cattle.
 And Pharaoh rose up in the night, he, and all his servants, and all the Egyptians; and there was a great cry in Egypt; for there was not a house where there was not one dead.
 And he called for Moses and Aaron by night, and said, Rise up, and get you forth from among my people, both ye and the children of Israel; and go, serve the LORD, as ye have said.
 Also take your flocks and your herds, as ye have said, and be gone; and bless me also.
 And the Egyptians were urgent upon the people, that they might send them out of the land in haste; for they said, We be all dead men.
Philo, Life of Moses (De Vita Moses) 1.143–1.146
(143) Such, then, were the afflictions and punishments by which Egypt was corrected; not one of which ever touched the Hebrews, although they were dwelling in the same cities and villages, and even houses, as the Egyptians, and touching the same earth and water, and air and fire, which are all component parts of nature, and which it is impossible to escape from. And this is the most extraordinary and almost incredible thing, that, by the very same events happening in the same place and at the same time, one people was destroyed and the other people was preserved.
(144) The river was changed into blood, but not to the Hebrews; for when these latter went to draw water from it, it underwent another change and became drinkable. Frogs went up from the water upon the land, and filled all the market-places, and stables, and dwelling-houses; but they retreated from before the Hebrews alone, as if they had been able to distinguish between the two nations, and to know which people it was proper should be punished and which should be treated in the opposite manner.
(145) No lice, no dog-flies, no locusts, which greatly injured the plants, and the fruits, and the animals, and the human beings, ever descended upon the Hebrews. Those unceasing storms of rain and hail, and thunder and lightning, which continued so uninterruptedly, never reached them; they never felt, no not even in their dreams, that most terrible ulceration which caused the Egyptians so much suffering; when that most dense darkness descended upon the others, they were living in bright daylight, a brilliancy as of noon-day shining all around them; when, among the Egyptians, all the first-born were slain, not one of the Hebrews died; for it was not likely, since even that destruction of such countless flocks and herds of cattle never carried off or injured a single flock or a single beats belonging to the Hebrews.
(146) And it seems to me that if any one had been present to see all that happened at that time, he would not have conceived any other idea than that the Hebrews were there as spectators of the miseries which the other nation was enduring; and, not only that, but that they were also there for the purpose of being taught that most beautiful and beneficial of all lessons, namely, piety. For a distinction could otherwise have never been made so decidedly between the good and the bad, giving destruction to the one and salvation to the other.
Source: Yonge, Charles Duke. The Works of Philo. Complete and Unabridged, New Updated Edition. David M. Scholer, editor. Hendrickson Publishers, 1993. ISBN 0943575931.