Citric acid is obtained from the juice of the lemon, Citrus limonum, or of the lime, Citrus bergamia, by neutralizing the boiling juice with chalk, and putting it through various processes. It is very soluble in water, and gr. xx. in 3 ss. of water makes a solution resembling lemon juice in strength and acidity.

Citric acid, like the other free acids, acts directly on the contents of the alimentary canal, neutralizing alkalies.

It is stimulant; relieves thirst and promotes appetite; increases the flow of the saliva and of the gastric juice, and, indirectly, increases the action of the kidneys and skin, hot lemonade especially being a diaphoretic.

It is slightly laxative, and counteracts a tendency to torpidity of the liver. The juice of half a lemon, mixed with that of an orange, is a satisfactory laxative drink in many cases. It is best taken before breakfast.

In malarial countries lemon-juice is freely used as an article of food, and among sailors and soldiers it is used as a prophylactic against scurvy.

Citric acid has no action on the sound skin; it is but slightly irritating in large quantities internally, and is not poisonous.

It may not be out of place here to refer to a popular error regarding a point of diet: that is, that a nursing woman may not drink lemonade because it will "sour the milk," and "give the baby colic." A nurse will probably often be appealed to on this subject. Her knowledge of the chemical facts - that citric acid is decomposed in the blood, forming a neutral salt; that it does not reach the tissues as an acid, but passes out of the body as a carbonate - will at once decide the question.