[47] It should not be inferred from this that mother's milk is the best under _all_ circumstances. It not infrequently happens that a mother, disregarding all indications to the contrary, will continue to nurse her baby after it has become disastrous both to herself and the infant to do so. If a baby remains puny, and the mother is exhausted and languid without any known cause, it is the part of wisdom to call in the aid of a physician, and have the milk analyzed. Good and careful feeding is infinitely better than nursing a baby upon impoverished milk, even if the quantity seems sufficient. A mother, in nursing her child, should do so at stated regular intervals. If it is injurious for a grown person to eat at odd times all day long, it is far more injurious for an infant. It will not hurt a child to be occasionally hungry, or even to cry, whereas it _will_ hurt it seriously and perhaps induce life-long dyspepsia if food is introduced into the stomach while there yet remains in it that previously taken in an undigested, or partly digested, condition. The cry which a young mother thinks indicates hunger, and hopes to allay by feeding, is often only a dyspeptic pain, which is increased by the very means she takes to lessen it. [48] The milk of goats and asses is said to be more easily digested than cow's milk, but is procurable only in exceptional cases. [49] From Uffelmann's "Hygiene of the Child." [50] See chapter on Milk. [51] Vessels for holding milk may be made sterile by boiling them in water for fifteen minutes. Glass is best. [52] A low temperature retards the growth of micro-organisms. [53] Test for reaction, fat, and specific gravity. See article on Milk. [54] The following mineral substances occur in both cow's and woman's milk: potassa, soda, lime, magnesia, iron, phosphoric acid, sulphuric acid, and chlorin. [55] It is worthy of notice, in this connection, that children have been known to be made ill by drinking water which has stood for a length of time--such water containing great numbers of bacteria, but none of the so-called _disease-producing_ organisms. The same water, when boiled, produced no ill effects. [56] Stated by Sedgwick. [57] Welsh. [58] Since writing the above I have learned that Prof. Vaughan has isolated a poisonous matter--the product of the growth of certain organisms which multiply readily in milk--which caused active vomiting, purging, collapse, and death when injected into the lower animals.