56 MATERIA MEDIC A AND THERAPEUTICS. 



The chloride, bicarbonate, or lactate formed in the sto- 

 mach, and the sulphate of magnesia directly given, having 

 reached the intestine, are very slowly absorbed, and if in 

 sufficient quantity, produce very marked local effects as saline 

 purgatives, the sulphate being hydragogue in its action. The 

 result is the free evacuation of a quantity of water by the 

 bowel, and with it the whole, or almost the whole, of the mag- 

 nesia. Sulphate of magnesia (Epsom salt) is our most common 

 saline purgative, used in the form of Mistura SennaB Composita 

 (black draught), of a simple solution in sulphuric acid and 

 water with some carminative, and of several of the popular 

 aperient waters, such as Friedrichshall, Piillna, Hunyadi 

 Janos, of all of which it is an important constituent. Sulphate 

 of magnesia is regarded as a mild, painless, non-nauseating 

 purgative, less rapid in its action than the soda salt, to be 

 used for completing the effect of purgative pills, for congestion 

 of the portal system, for chronic constipation as an habitual 

 laxative in combination with other salts in the above-named 

 waters, and for feverish attacks with loaded bowels. 



Magnesia and the carbonates, when used as purgatives, are 

 chiefly given to children in diarrhoea with foul acid stools, very 

 frequently in the form of Pulvis Ehei Composita (Gregory's 

 Powder). In small doses, neither salt has any purgative action 

 on the bowel, but enters the blood. 



2. ACTION ON THE BLOOD AND ITS USES. 



Entering the circulation as the chloride or lactate, magnesia 

 increases the natural alkalinity of the plasma, of which it is a 

 normal constituent, and helps to hold in solution any acid 

 which may be in excess. It will therefore be useful in gout, 

 lithiasis, and possibly in chronic rheumatism, to assist the more 

 powerful alkalinisers of the blood with which it is combined in 

 the waters of Ems, Baden-Baden, Aix-les-Bains, Carlsbad, etc. 



3. SPECIFIC ACTION AND USES. 



Magnesia taken medicinally does not exert any appreciable 

 effect upon the tissues or nutrition generally. Although an 

 important constituent of bone, it cannot be said to be of any 

 value in rickets or other diseases in which the osseous tissue is 

 deficient in solid matter. 



4. REMOTE LOCAL ACTION. 



When magnesia does not purge, it is excreted chiefly by 

 the kidneys, rendering the urine more abundant and less acid, 

 and dissolving uric acid. Its diuretic and alkalinising effects 

 contribute to the value of magnesia waters in gout and gravel. 



