Cappello de Certitudine Capite Collati Baptismi
This came in handy on the Catholic Answers Forums the other day regarding a question about whether water had to be poured over the head in baptism.
Tractatus Canonico-Moralis de Sacramentis by Felix Cappello (Vol. 1, Fourth edition, p. 105) says this:
1 Aqua immediate tangere debet corpus baptizandi. Id ex ipso conceptu et fine ablutionis liquet. Nomine capitis intelligitur frons, vertex, visus.
Invalidus est Baptismus, si, prole nondum in lucem edita, matris corpus abluatur; item, si aqua tangat solum vestes baptizandi; validus, contra, est Baptismus, si aqua effundatur super caput crusta ulcerosa opertum aut sordibus ante lotionem adhuc obductum, quia corpus vere tangitur.
Dubius est Baptismus collatus super secundinam, i.e., super membranam qua usque ad partum infantis corpus involvitur.
Baptismus collatus super crines validus est, quia crines revera ad corpus pertinent ideoque, dum ipsi abluuntur, caput vere proprieque abluitur. Contraria opinio quavis caret solida probabilitate; quare attendenda non est.
2 Aqua super caput effundi debet. Id affirmatur, ut certa omnino sit validitas Baptismi. Probabilissime est validus Baptismus, speculative loquendo, si in alia notabili corporis parte, ex. gr., in pectore, vel scapulis, puer ablatus fuerit. Tamen certum omnino est, Baptismum in casu habendum esse practice ut dubium, et consequenter sub conditione postea repetendum.
My translation:
1 The water should directly touch the body of the person to be baptized. This is proved from the concept and purpose of washing. By the name head is understood the forehead, the crown, it seems.
Baptism is invalid, if, while the child has not yet been drawn into the light [read "born"], the body of the mother is washed; likewise, if the water only touches the clothes of the person to be baptized; Baptism is valid, on the other hand, if the water is poured over the head covered over by scabs or drawn out [read "delivered"] still covered in filth before being washed, because the body is truly touched.
Baptism is doubtful if conferred over the amniotic sac, i.e., over the membrane in which the body of an infant is wrapped up even till birth.
Baptism conferred over the hair is valid, because the hair in fact pertains to the body therefore, when it is washed, the head is truly and properly washed. Whatever opinion there is to the contrary lacks solid probability; therefore it should not be regarded.
2 The water should be poured over the head. This is affirmed, so that there might be the altogether certain validity of Baptism. Baptism is very probably valid, speculatively speaking, if the child is washed on other notable body parts, e.g., on the chest or shoulders. Nevertheless it is altogether certain, that Baptism in that case should be regarded practically as doubtful, and consequently should afterward be repeated under condition.
