SALINES 253 



its concentration approximates that of the blood. The distention of 

 the intestines by the fluid stimulates peristalsis, both in the large 

 and small intestines. 



The cathartic salts are not absolutely non-absorbable, and so if 

 peristalsis is prevented by some means, their solutions may be almost 

 completely absorbed into the blood and cause diuresis if the absorp- 

 tion has been sufficiently rapid, because the renal epithelium is per- 

 meable to these salts. On the other hand, those salines which are 

 rapidly absorbed act as diuretics, since they withdraw fluid from 

 the tissues into the blood, and consequently increase blood pressure 

 in the kidneys. Furthermore, they are readily diffusible to the 

 epithelium of the kidneys. 



There is considerable controversy concerning just how the pur- 

 gative action of salines takes place, but it is believed to be due, 

 almost if not entirely, to their physical relation to the tissues 

 (osmotic properties). 



In the first place, they increase the fluid in the intestinal canal. 

 For instance, if an isotonic solution of epsom salts is injected into 

 a loop of intestine, very little secretion or absorption occurs, so that 

 after a few hours' time the same amount of salt and liquid may be 

 obtained. If stronger, hypertonic solutions are used, the fluid in 

 the loop will be increased on account of osmotic action. The pres- 

 ence of these non-absorbable salts in the intestines prevents the nor- 

 mal absorption of fluid, and hence a much larger amount will reach 

 the large intestine and the contents of the bowel will necessarily be 

 more fluid. The increased amount of fluid causes distention of the 

 bowel and this will stimulate peristalsis. Isotonic and hypotonic 

 solutions of the cathartic salts will prevent absorption but only con- 

 centrated hypertonic solutions draw fluid from the tissues and blood 

 and may fail to cause purgation if the blood tissues contain very lit- 

 tle fluid, as has been shown in experimental work on animals which 

 have been deprived of water for a few days previously ; but, on the 

 contrary, where large quantities of fluid are present in the system, as 

 in edema, the salines, administered in concentration (hypertonic 

 solutions), produce purgation readily by drawing fluid indirectly 

 through the blood into the bowel. It is on account of the fact that 

 hypertonic (concentrated) solutions must get their water from 

 the tissues, that they require much longer to produce their action 

 than weak solutions, and consequently, unless it is desired to remove 

 a large amount of fluid from the body, as in edema, they should be 

 given well diluted and the animal allowed plenty of water. 



The salines prove very serviceable for ruminants and small ani- 

 mals, but are, not especially dependable in equine medicine. 



