ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 285 



urine after being fed 10 to 15 grams of starch paste, while a 

 healthy dog will stand several times this amount at a single 

 feeding and not excrete sugar. 1 Most striking is the assimi- 

 lation limit of one and the same animal for different kinds of 

 carbohydrates. Ordinary starch leads all the others in the 

 amount that may be consumed in twenfy-four hours (more 

 than 500 grams) without the appearance of sugar in the 

 urine. Next in order stand dextrose, laevulose, sucrose, mal- 

 tose, and lactose in the order named. The reason why the 

 disaccharides stand lowest is no doubt to be sought in the 

 fact that when these are fed rapidly and in large 'amounts, 

 they pass without change into the blood, and since the liver 

 and muscles retain the disaccharides but imperfectly their 

 concentration in the blood soon exceeds the limits at which 

 the sugar passes over into the urine. 



The rapidity with which the different sugars are absorbed 

 seems not at all dependent upon their rates of diffusion or 

 differences in osmotic pressure. The subject has been investi- 

 gated by ALBERTONi, 2 ROHMANN and NAGANO. 3 Sugars are 

 absorbed not only from solutions which are hypertonic or iso- 

 tonic with the blood but also such as are hypo tonic. When 

 isosmotic solutions of sugars are compared it is found that dex- 

 trose is absorbed most rapidly, sucrose next, and much more 

 slowly lactose. But the amount absorbed in any unit of time 

 varies, much more of any given sugar being absorbed in the 

 first hour after feeding than in subsequent hours. Starch, 

 as already pointed out, cannot be absorbed as such. Its 

 absorption is dependent upon the velocity with which it is 

 split into absorbable sugars. These sugars under normal 

 circumstances are absorbed as rapidly as formed. Since the 

 amount of amylolytic change is greatest not immediately 

 after eating but in the second or third hour of the digestive 



1 My own attempts to repeat this experiment succeeded only once 

 on one out of four dogs. 



2 ALBERTONI: Centralbl. f. Physiol., 1901, XV, p. 457. 



3 ROHMANN and NAGANO: Centralbl. f. Physiol., 1901, XV, p. 494. 



