48 PHYSIOLOGY OF ALIMENTATION. 



were effective. Magnesium sulphate is about as active a 

 cathartic as sodium sulphate, but it is by no means as harm- 

 less as the latter. MACCALLUM found that magnesium sul- 

 phate was often fatal in doses in which sodium sulphate is 

 entirely harmless. This statement is confirmed by some of 

 my own experiments on glycosuria, in which it was found that 

 the action of the sulphate of sodium is less harmful than that 

 of 'magnesium. The poisonous action is apparently deter- 

 mined by the magnesium constituent in the latter salt, which 

 has a powerful effect upon the heart. A practical conclusion 

 to be drawn from this is that it is better to give the sodium 

 salt to patients than the magnesium salt. The intensely 

 poisonous action of the barium chloride should also put a ban 

 upon the use of this drug in medicine. The fluoride and 

 oxalate also have specific poisonous properties which speak 

 against their use in medicine, especially when apparently 

 harmless salts may be employed with just as good results if 

 only care be taken to use the right amounts. 



The purgative action of the saline cathartics depends upon 

 yet another factor than the mere increase in the peristaltic 

 movements of the intestine, namely, an increased secretion 

 of fluid into the intestine. This fact was observed by GUMI- 

 LEWSKI l and R6HMANN, 2 and is confirmed by MACCALLUM'S 

 observations. If a loop of intestine is tied off and a saline 

 cathartic is injected subcutaneously or intravenously, or is 

 simply painted on its surface, a secretion of fluid into the 

 loop of intestine is observed in addition to the increased 

 peristalsis. 



MACCALLUM has been able to show that the effect of the 

 saline cathartics enumerated above, both in bringing about 

 an increased peristalsis and an increased secretion of fluid 

 into the intestine, can be counteracted by calcium chloride r 

 and to a less extent by strontium and magnesium chloride. 

 This antagonism between sodium and calcium salts seems to 



1 GUMILEWSKI: Pfliiger's Archiv, 1886, XXXIX, p. 556, 



2 RQHMANN: Pfliiger's Archiv, 1887, XLI, p. 411. 



