Laudator Temporis Acti

Jerome, Homilies 51.5 (Corpus Christianorum, Series Latina, Vol. LXXVIII, p. 305; tr. Marie Liguori Ewald):

If a physician should notice infected and decayed tissue in a body and say, 'What concern is that of mine?' you would conclude rightly that he is cruel; but if he should excise the infected tissues and cauterize the wound, he is compassionate, for he is saving the life of a man. Likewise, a teacher, if he dismisses a lad and does not exact obedience from him, hates him; if, on the other hand, he disciplines him and the remedy cures him, his apparent severity turns out to be clemency.

Si uiderit medicus in corpore carnes putridas, et dicat, Quid ad me pertinet? scias quia crudelis est. Si autem praecidat, et cauterium inponat, misericors est, quia saluat hominem. Similiter et magister si dimittat puerum, et non eum exigat disciplinam, odit eum. Si autem exigat, et medicus curet, quae putatur esse asperitas, clementia est.

I would alter the last part of the translation as follows:

if, on the other hand, [the teacher] exercises discipline and the physician effects a cure, the apparent severity turns out to be clemency.

I also modified the punctuation of the Latin — here is an image of the CCSL text: For the double accusative "eum exigat disciplinam," see Thesaurus Linguae Latinae 5,2:1458,24 (exigo c. dupl. acc; this example not cited).