"Sink deep or touch not the Cartesian spring!"

(300.9-302.10)  Kevin, still unhappy about Dolph's geometry lesson, begins today's reading itching to have the last word on the subject.  Before doing so, he eats a Jacob's marie biscuit.  In another echo of language from Yeats' A Vision, Dolph (the "Other") continues to use his creative mind to "deleberate the mass from the booty of fight" (in one sense, devilishly liberate the masses from the beauty of light) while Kevin (the "Same") tries to use the bounty of food (that biscuit he just enjoyed) to "delubberate the mess from his corructive mund" (in one sense, eliminate the mess (the knowledge he received from Dolph) from his corrupted mind).  

Kevin's angry:  all of this math homework (especially here, the trigonometry) and Dolph's lecturing has got him in a state where the veins of his neck are bursting out like tightropes.  The narrator calls for a doctor in a parenthetical:  "(Spry him!  call a bloodlekar!  Where's Dr Brassenaarse?)".  But it's Kevin's lot in life for him to suffer.  As for his buffoonish brother Dolph, who is late for mass, Kevin tells us to "pray for blaablaablack sheep."

At this point, the narrator (in another parenthetical) tries to soothe Kevin, telling him that he could write anything as fine as his father ("that moultylousy Erewhig"), and exhorting him to best his brother:  "Nock the muddy nickers!"  The remainder of the passage is a kind of letter, which, McHugh points out, recalls some of the language from the letter of ALP that was found in the dump by the hen.  While Campbell and Robinson indicate that the letter contains at least the voices of both brothers and their sister (taking cues from Shem's comments in the left margin), I'm having a hard time seeing this, and so I'm operating on the basis that the letter is written entirely by Kevin.  (I could easily be swayed otherwise, though.)  He's addressing his lady, beginning with a "how are you, waggy?", and then noting how his soul is "sorrafool."  His subject turns to his brother, Jerry who is also a sad fellow, and a "mister-mysterion."  In his anger, Kevin interrupts his description of Jerry's sorry state to directly address his brother to tell him to snap out of his funk:  "Sink deep or touch not the Cartesian spring!  Want more ashes, griper!"  Returning to the letter, Kevin asks his lady to lend him some money, although I admit this could be Kevin mocking his down-and-out brother.  Finally, wrapping up the letter, Kevin returns to his cutesy language, saying, "Well wiggywiggywagtail, and how are you, yaggy?" before singing his letter "Blott."