All of it is from St. Thomas except the explanation in this type of brackets [ ] which I think was added by the translator:
St. Thomas Aquinas on loss of jurisdiction by heretics:
Summa, 2a 2ae, q. 39, art. 3. (Utrum schismatici habeant aliquam potestatem)
“...Potestas autem iurisdictionis est quae ex simplici iniunctione hominis confertur; et talis potestas non immobiliter adhaeret; unde in schismaticis et haereticis non manet; unde non possunt nec absolvere, nec excommunicare, nec indulgentias facere, aut aliquid huiusmodi; quod si fecerint, nihil est actum.”
(Whether schismatics have any power.)
“...The power of jurisdiction, however [as opposed to the power of Orders, which he has just discussed], is that [power] which is conferred simply by the injunction of man; and this power does not adhere immovably; therefore it does not remain in schismatics and heretics. Hence they can neither absolve, nor excommunicate, nor grant indulgences, or anything of this sort. If they do this, the act is null.”