The professor saw this and wished to startle him.
"Eh, there, sleepy-head! What's this?
Lazy, too, so it's sure you [30] don't know the lesson, ha ?" Padre Millon not only used the depreciative _tu_ with the students, like a good friar, but he also addressed them in the slang of the markets, a practise that he had acquired from the professor of canonical law: whether that reverend gentleman wished to humble the students or the sacred decrees of the councils is a question not yet settled, in spite of the great attention that has been given to it.
This question, instead of offending the class, amused them, and many laughed--it was a daily occurrence.

But the sleeper did not laugh; he arose with a bound, rubbed his eyes, and, as though a steam-engine were turning the phonograph, began to recite.
"The name of mirror is applied to all polished surfaces intended to produce by the reflection of light the images of the objects placed before said surfaces.

From the substances that form these surfaces, they are divided into metallic mirrors and glass mirrors--" "Stop, stop, stop!" interrupted the professor.

"Heavens, what a rattle! We are at the point where the mirrors are divided into metallic and glass, eh?
Now if I should present to you a block of wood, a piece of kamagon for instance, well polished and varnished, or a slab of black marble well burnished, or a square of jet, which would reflect the images of objects placed before them, how would you classify those mirrors ?" Whether he did not know what to answer or did not understand the question, the student tried to get out of the difficulty by demonstrating that he knew the lesson, so he rushed on like a torrent.
"The first are composed of brass or an alloy of different metals and the second of a sheet of glass, with its two sides well polished, one of which has an amalgam of tin adhering to it." "Tut, tut, tut! That's not it! I say to you '_Dominus vobiscum_,' and you answer me with '_Requiescat in pace!_' " The worthy professor then repeated the question in the vernacular of the markets, interspersed with _cosas_ and _abas_ at every moment.
The poor youth did not know how to get out of the quandary: he doubted whether to include the kamagon with the metals, or the marble with glasses, and leave the jet as a neutral substance, until Juanito Pelaez maliciously prompted him: "The mirror of kamagon among the wooden mirrors." The incautious youth repeated this aloud and half the class was convulsed with laughter.
"A good sample of wood you are yourself!" exclaimed the professor, laughing in spite of himself.

"Let's see from what you would define a mirror--from a surface _per se, in quantum est superficies_, or from a substance that forms the surface, or from the substance upon which the surface rests, the raw material, modified by the attribute 'surface,' since it is clear that, surface being an accidental property of bodies, it cannot exist without substance.