This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Cryer says that mothers or nurses in caring for the infant "will give attention to dirty hands or face and bathe the body daily, but how few keep the mouth as clean! The teeth should be gently and thoroughly brushed with a small soft tooth brush as soon as they make their appearance.... Fermentation of residual portions of milk remaining in the mouth of the infant after feeding is a prolific source of gastric curd, intestinal irritation, giving rise to colic and diarrhoea. The mouth of the child should therefore be kept carefully cleansed, and before each feeding be washed out with a solution of boric acid in distilled water applied on a soft linen rag".