354 STUDIES IN ADVANCED PHYSIOLOGY. 



the blood is saltier than the pure water, and so the water 

 in osmotic currents flows into the blood. On the other 

 hand, if sufficient salty water should have been drunk and 

 the contents of the alimentary canal become saltier than the 

 blood, water would run from the blood into the alimentary 

 canal and the thirst be exaggerated. These osmotic cur- 

 rents explain the physiological action of certain salts which 

 are sometimes prescribed by the physician. Such mineral 

 salts, usually Epsom salts, increase the saltiness in the in- 

 testine so greatly that currents of water from the blood pass 

 into the intestine and thus produce the medicinal effects of 

 that drug. On the other hand, if these salts were injected 

 into the blood and the saltiness of the blood thereby materi- 

 ally increased, larger quantities of water than usual would 

 be absorbed from the intestine and so constipation produced 

 or exaggerated. 



To trace out in detail these processes of absorption, it 

 may be desirable to treat of each class of foods separately. 

 It is not necessary to call attention to the absorptive pro- 

 cess in the various portions of the alimentary canal, because 

 experiments conclusively show that practically all the ab- 

 sorption occurs in the small intestine. It seems a little re- 

 markable at first to find that practically no absorption at all 

 occurs in the stomach. Experiments have been made over 

 and over again to show that dialyzable substances, even 

 water itself, are absorbed in very small quantities indeed 

 from the stomach. As a digestive agent it has an import- 

 ant role, but as an absorbing organ it figures little indeed. 

 Experiments have been tried on animals by injecting water 

 into the stomach and keeping it there an hour or more, and 

 then determining how much of it had been absorbed in the 

 meantime. Such experiments show that but a trifling 

 amount is thus absorbed. We have to imagine, therefore, 

 that nearly all of the liquids and dialyzable substances 

 which we take into the stomach and which seem to reach 

 the blood so quickly are at once passed by the stomach into 

 the duodenum and absorbed from that place. Even alcohol 



