There seems no reason to doubt that intestinal proteolysis is designed to disrupt the protein molecule completely into its constituent aminoacids before absorption occurs.
It has long been recognized, however, that under the influence of disease or through procedures in the experimental laboratory protein not completely digested may be absorbed from the intestine and enter the body fluids. Most of the earlier observations were made on experimental animals, but it also was demonstrated that such absorption may occur in infants who have nutritional disorders or are fed excessive amounts of protein foods.
The earlier literature was reviewed by Lawatschek,1 Moro,2 Bauer,3 Ascoli and Vigano,4 Michaelis and Oppenheimer,5 Ganghofner and Langer,6 Hamberger and Sperk,7 Lust,8 Hayashi,9 Schloss and Worthen10 and Anderson and Schloss.11 Recently the literature was thoroughly reviewed by Ratner and Gruehl.12
In 1926 Walzer13 showed by
LIPPARD VW, SCHLOSS OM, JOHNSON PA. IMMUNE REACTIONS INDUCED IN INFANTS BY INTESTINAL ABSORPTION OF INCOMPLETELY DIGESTED COW'S MILK PROTEIN. Am J Dis Child. 1936;51(3):562–574. doi:10.1001/archpedi.1936.01970150066004