436 CHEMISTRY OF THE DIGESTIVE PROCESSES. 



Ingestion of large quantities of solution of sugar leads to the appear- 

 ance of sugar in the urine (alimentary glycosuria), due to the assimilation 

 of the sugar not keeping pace with its absorption. 1 Absorption itself 

 is also disturbed by the appearance of diarrhoea. But when carbohydrate 

 is introduced into the alimentary canal, in the form of starch, immense 

 quantities can be rapidly and completely absorbed without any glycosuria 

 or other disturbance ensuing. 



Thus Kiibner 2 found that a man consuming a daily ration of 508-670 

 grins, of carbohydrate contained in wheaten bread, left unabsorbed only 

 0'8-2'6 per cent. ; of the carbohydrate of peas (357-588 grins.) 3'6-7'0 per 

 cent, was unabsorbed; and of potatoes (718 grins.) 7'6 percent. This 

 complete absorption and utilisation of carbohydrate, when taken in the 

 form of starch, is probably due to the ra^te of assimilation and storage as 

 glycogen in the liver, being able to keep pace with that of absorption 

 from the intestine. 



Conditions of absorption of proteids. The power possessed by 

 the intestinal cells of absorbing various forms of proteid affords one 

 of the best illustrations that this process is not one of mere 

 physical diffusion. The products found towards the end of a proteid 

 digestion in vitro are distinguished from the .proteids from which they 

 originate by being slightly diffusible. To this fact great importance 

 was at one time attributed, because it was thought that only proteids 

 in a diffusible form were capable of absorption, and hence that peptonisa- 

 tion was in all cases a necessary preliminary. It is now generally 

 admitted that many forms of native proteid are capable of entering the 

 epithelial cells without previous change by digestion or otherwise ; and 

 in those cases in which a proteid is incapable of direct absorption a much 

 less profound change than peptonisation is sufficient to render it so, 

 namely, conversion into acid or alkali albumin. Such an absorption of 

 soluble proteid, other than albumose or peptone, takes place not only in 

 the small intestine, but in the large intestine, and even in the rectum. 



Voit and Bauer 3 cleared a loop of small intestine of its contents as 

 completely as possible by stroking, and separated it from the rest of the 

 gut by double ligatures at each end. Various forms of proteid, in solu- 

 tions of known amount and strength, were then injected into this loop ; 

 the intestine was replaced, and its contents examined on killing the 

 animal (cat or dog) some hours later. It was found that variable amounts 

 of these proteids had disappeared; thus, in one to four hours, 16-33 per 

 cent, of white of egg had disappeared, and of syntonin from ox muscle 

 28-95 per cent. It might be supposed that the portion of proteid ab- 

 sorbed had been peptonised by traces of proteolytic enzyme which might 

 be present in the intestine ; but in the unabsorbed proteid remaining at 

 the end of the experiment, no albumose or peptone was found. Voit and 

 Bauer also injected solutions of white of egg and sodium chloride into the 

 rectum of man and animals in a fasting condition, and found a marked 

 increase (6 to 8 grms. in 24 hours) in the amount of nitrogen eliminated 

 by the kidneys ; in fact, an equilibrium of nitrogenous metabolism may 

 even be maintained in this way. It has been shown by Eichhorst, 4 who 

 confirms these results, that no appreciable amount of peptonisation takes 



1 C. Voit, Ztschr. f. iol., Miinchen, 1891, Bd. xxviii. S. 245. 



2 Ibid., Bd. xix. S. 45. 



3 Ibid., Bd. v. S. 562. 



4 Arch.f. d. ges. PhysioL, Bonn, 1871, Bd. iv. S. 570. 



