48 MATERIA MEDICA AND THERAPEUTICS. 



alimentary canal very similar to that of potash, but it is not 

 used for this purpose directly. 



2. ACTION ON THE BLOOD, AND ITS USES. 



Lithium enters the "blood, and behaves there much like 

 potash, increasing its alkalinity, and combining with such 

 acid bodies as uric acid, for which it has a powerful affinity, 

 (1 part of a solution of the carbonate of lithia, at 38 C., dis- 

 solving four parts of the acid). It is extensively used in gout, to 

 hold this substance in solution, and thus prevent acute attacks 

 by fresh deposit in the tissues. 



3. SPECIFIC ACTION AND USES. 



In this respect also lithia closely resembles potash, being a 

 cardiac and nervo-muscular depressant, if given in large doses 

 or for a length of time ; but the risk of lithia poisoning is too 

 small to be allowed to interfere with the exhibition of the drug 

 in suitable cases. 



4. REMOTE LOCAL ACTION AND USES. 



Lithium is rapidly excreted by the kidneys, and prob- 

 ably by the mucous membranes. It is a powerful diuretic in 

 passing through the renal epithelium ; and whilst increasing 

 the volume of water, it diminishes its acidity, and holds in 

 solution even an excess of uric acid. It is accordingly used as 

 a valuable remedy in gout, as it hastens the excretion of the 

 products which it dissolves in the blood ; and in acid lithiasis 

 or gravel, where it prevents the deposit of salts in the kidney 

 and urinary passages. 



Both of the salts of lithia may be used, the only important 

 difference between them being with respect to their solubility, 

 which is very marked. 



CALCIUM. Ca. 40. LIME. 



Creta or chalk is naturally discussed along with 

 calcium or lime, of which it is the carbonate. 



The various preparations of lime may be repre- 

 sented as follows, according to their source. 



1. Creta. Chalk. CaC0 3 (impure). Native. 

 From Creta are made : 



a. Greta Praeparata. Prepared Chalk. CaC0 3 

 (nearly pure). 



