Work which we previously carried out in vitro1 showed that under all conditions which we studied cow's milk and certain modifications of it were digested with greatest speed and completeness at a ph of 4.5 when rennin2 was present in the artificial gastric juice.
The milks which we studied were untreated cow's milk, Carnation milk, Mead's powdered milk, Mead's lactic acid milk, Mead's protein milk and buttermilk. We also studied the effect of adding rennin to cow's milk, Carnation milk and powdered milk. Since in our experiment in vitro we found that the addition of rennin to acid milks did not increase tile speed of digestion as much as its addition to nonacid milks, we did not add rennin to the acid milks studied in vivo.
We wished to see how the digestion of the milk mixtures which we had studied in vitro compared with the digestion