MECHANICAL PHENOMENA. 47 



eighth molecular l sodium citrate solution are injected into 

 the lumen of the intestine of a rabbit, increased peristaltic 

 movements manifest themselves in 10 to 15 minutes. About 

 the same length of time is required when the same amount of 

 this salt solution is injected subcutaneously. When, how- 

 ever, only 1 to 2 c.c. of this sodium citrate solution are 

 injected intravenously, a striking increase in intestinal move- 

 ments is visible in one to two minutes. It almost seems from 

 these experiments that the saline cathartics must be ab- 

 sorbed from the intestinal tract before they can produce their 

 specific effects. A reaction in the form of a local constriction 

 of the musculature of the gut is obtained almost immediately 

 after painting one of the saline cathartics on the peritoneal 

 coat of the intestine. 



When equimolecular 2 solutions are compared, it is found 

 that by far the most powerful of the cathartics listed above 

 is barium chloride, after which come the citrate, fluoride, 

 sulphate, tartrate, oxalate, and phosphate of sodium, the 

 intensity of the action of which decreases approximately in 

 the order named. The intravenous injection of a solution con- 

 taining a few milligrams of the dry salt is sufficient to bring 

 about powerful contractions of the intestine. The power of 

 the various salts to produce their cathartic action was deter- 

 mined by discovering the lowest concentration in which they 



1 That is, a solution of sodium citrate made by dissolving one gram- 

 molecule of the dry salt in enough water to make eight litres. A gram- 

 molecule of a substance is the molecular weight of that substance (plus 

 the molecular weight of its water of crystallization, if it has any) ex- 

 pressed in grams. 



2 That is, solutions containing the same number of gram-molecules of 

 the various salts dissolved in the unit volume of the solvent (water in 

 this case). The comparison of equal percentage solutions, that is 

 solutions containing the same weight of the salts in the unit volume of 

 solvent, as was generally done by the older observers, leads to entirely 

 erroneous conceptions of the relative activity of the dissolved salts. 

 It would be well if all workers in experimental medicine would employ 

 only chemically equivalent solutions. 



