_Acids._--In those forms of sleeplessness which are dependent upon disordered conditions of the digestive apparatus, acids are often useful. Their topical effects upon the mucous membrane of the stomach are stimulant and alterative; hence they are useful in atonic dyspepsia, where there is deficient secretion of the gastric juice. In such cases _hydrochloric acid_ and _lactic acid_ are useful. The first should be given, in doses of five drops diluted with half a pint of water, after each meal. Lactic acid may be given in doses of one or two teaspoonfuls, similarly diluted. It has been asserted, on theoretical grounds, that lactic acid and the lactate of sodium are directly hypnotic, but its experimental use has never given satisfactory results. _Phosphoric acid_ has been used in the same way, with very similar effects. An impure solution of phosphoric acid, known as _Horsford’s Acid Phosphate_, has been extensively used for its supposed hypnotic properties. It assists digestion, stimulates the kidneys, and by its general diffusion promotes molecular activity throughout the body. It is thus indirectly beneficial in cases of insomnia. No small part of the benefits thus obtained must, however, be ascribed to the water with which these acids are diluted. When the liver becomes sluggish in its action, nitric acid, in doses of five drops diluted with half a pint of water, may be taken every four hours with great advantage. Thus used, the mineral acids may often yield invaluable service in the treatment of insomnia occasioned by cachectic conditions of the body--notably such as are produced by malaria, oxaluria, and the so-called phosphatic and rheumatic diatheses. NERVOUS SEDATIVES. The remedies thus far considered are but indirectly hypnotic in their effects, though exceedingly valuable as agents for the production of conditions favorable to sleep. We may now pass to the consideration of a class of remedies which operate more directly upon the brain to depress its energy. They are, therefore, called nervous sedatives, and they include the majority of narcotic substances. _Cold._--The operation of cold upon the body has already been sufficiently considered. It only remains to note the effects of cold applied through the agency of baths and local refrigerants. A full account of the theory and practice of hydrotherapeutics can be found in the second volume of Von Ziemssen’s _Handbuch der Allgemeinen Therapie_. The English reader will find the subject treated at sufficient length in Ringer’s _Handbook of Therapeutics_. According to Ringer, the sitz-bath, taken at a temperature between 60° and 80° F., is very useful to soothe “an irritable restless state of the nervous system.” It should be employed once or twice a day, from five to thirty minutes at a time. Among other beneficial consequences is the promotion of quiet sleep.