50 PHYSIOLOGY OF ALIMENTATION. 



So far as the quantitative relation is concerned which 

 exists between the dose of a saline purgative sufficient to 

 affect the intestine and that of calcium chloride sufficient 

 to suppress the increased peristalsis and intestinal secretion 

 brought about by the former, it may be said that a chemically 

 equivalent amount of the one just counteracts the other. 

 If, for example, a certain number of cubic centimeters of a 

 1/8 molecular sodium citrate solution are injected into a 

 rabbit it requires an equal volume of a 1/8 molecular calcium 

 chloride solution to counteract the effect of the former. This 

 counteraction takes place almost immediately if the calcium 

 chloride is applied to the peritoneal coat of the intestine. 

 If the calcium chloride is injected intravenously it shows 

 its specific effect in one to two minutes, but it takes ten to 

 twenty minutes if it is injected subcutaneously or into the 

 lumen of the intestine. 



MACCALLUM is inclined to explain the action of the saline 

 purgatives through their power of diminishing the concen- 

 tration of the free calcium ions in the tissues upon which 

 these cathartics act. This is the same explanation that LOEB 

 gives of the twitchings observed by him when voluntary 

 muscles are immersed in these same salt solutions. The 

 addition of a calcium salt therefore counteracts the effect of 

 the saline cathartics by restoring the concentration of the 

 calcium ions and so bringing the intestine back to its original 

 state. It must be remembered, however, that barium 

 chloride is the most powerful of all the salts studied, and 

 yet it is difficult to see how the administration of such traces 

 of this substance as are necessary to bring about a violent 

 catharsis is to be explained by its effects in reducing the 

 concentration of the free calcium ions. HOFMEISTER'S belief 

 that catharsis is brought about through the coagulation of 

 certain colloids by the cathartic salts seems less open to 

 objectionr- 



The movements of -the intestine, as a whole, under the 

 influence of saline cathartics have not yet been studied. 



