Experience shows that milk undergoes many changes. Science has studied these and finds they are effected by the presence of bacteria. Though milk has been experimentally obtained without any bacteria, it is not without bacteria as it comes into use. Bacteria usually multiply rapidly. Though all are not harmful, any bacteria consumed in large numbers undermine health and gravely affect the death-rate of infants.

Drs. Park and Holt find, of infants under I year, during 3 mos. in summer: None died that were fed human milk or certified milk of cows;

3% died of those fed pasteurized milk (treated to reduce bacteria);

9% " " bottled milk (protected thus from dairy);

20% " " condensed milk or loose milk sold open in bulk.

Milk feeds germs. Many that would not grow in water thrive in milk. Some produce harmless changes in milk as souring. Others change the milk itself dangerously; this happens when milk is kept under unsanitary conditions. A ferment may then enter it which produces a substance (tyrotox-icon) that causes serious, even fatal, intestinal disorders. It is this that happens when ptomaine poisoning occurs from cream, ice-cream, cheese. A third type of bacteria are themselves directly disease-producing and may grow in milk without changing its composition significantly. But when these enter the human body with the milk, they there cause detrimental changes in body-tissues. All bacteria cannot live thus, but those producing many human diseases can, such as those of dysentery, cholera, typhoid and scarlet fevers, diphtheria, tuberculosis.

Disease-producing Bacteria.

a, pus-producing; b, pneumonia; c, tuberculosis; d, tetanus (lockjaw). (Conn and Buddington) e and f, typhoid bacilli. (Pfeiffer) g, pus; h, dysentery. (Sleiger).