One of the best-known diseases caused by the absence of some essential of a diet is called scurvy. This used to be very common on board ships on long voyages, and was caused either by the great use of salt beef, or (much more probably) by the absence of fresh vegetables containing the necessary vegetable acids. Nowadays fresh meat can be more easily taken on long voyages, and potatoes and lime-juice are freely given, so that sea scurvy is practically unknown. In large towns, however, we very frequently see the same disease, as shown by the sore and bleeding gums and the appearance of blood under the skin like small bruises, and the condition is only found in badly-fed people, who will tell you that they live almost entirely on bread and butter and tea, with meat occasionally, and fresh vegetables sometimes on Sunday. This land scurvy soon disappears when proper food is given.

Rickets is a disease found in young children, and is very largely due to feeding with improper food (such as starchy materials,), and to an absence of fresh air. The child perspires chiefly about the head at night, and the whole body seems to be tender and sore, the ends of the bones becoming soft and enlarged, especially near the ankles and wrists, and deformities of the limbs, such as bow legs or knock knees, may result. If there is any sign of this disease beginning, the child must not on any account be allowed to walk for many months, and he should be given plenty of fresh air, sunlight, and good nourishing food.