During the first year, the average normal infant exhibits, at the height of digestion, a range of gastric acidity (Kronenberg,1 Marriott2) that lies between pH 3.5 and 5.0. Between this and the range of acidity required for the action of the gastric enzymes, as determined in vitro, there is an interesting relationship, of much significance in the physiology of infant digestion. Chart 1 presents graphically the facts discussed in a previous communication.3 Rennet, acting best between pH 6.3 and 6.0, curdles milk soon after ingestion, before the height of gastric acidity has been attained. Chymosin (van Dam), an enzyme with feeble proteolytic powers, about which little is known, acts best at pH 5.0. Gastric lipase and invertase (the latter studied, however, from yeast) are half active at about pH 6.0, and fully active between pH 4.5 and 4.0. Pepsin requires a much
FABER HK. HYDROCHLORIC ACID MILK IN INFANT FEEDING. Am J Dis Child. 1923;26(5):401–410. doi:10.1001/archpedi.1923.04120170012003
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