322 



DIGESTION 



thoroughly appreciated only in the last few years. It was observed in 

 earlier nutritional experiments that some rats receiving a diet deficient 

 in B complex vitamins would recover spontaneously from the deficiency 

 without supplementation of the diet with the missing vitamins. Although 

 receiving a B vitamin deficient diet, other rats which were prevented 

 from eating their feces (coprophagy is a common practice in the animal 

 world) required much more supplementation with B vitamins than those 

 consuming feces. When rats are fed a purified diet to which all the 

 vitamins except folic acid have been added, they will develop normally; 

 however, when succinylsulfathiazole (which is not absorbed from the 

 intestines) is added to this ration, typical symptoms of folic acid de- 

 ficiency develop, and the amount of this vitamin in the cecal content 

 and various tissues decreases. It is thought that the sulfa drugs under 

 these conditions depress the bacterial synthesis of folic acid in the in- 

 testines. In contrast to the depression of vitamin production by an anti- 

 bacterial agent described above, it has been found more recently that 

 the addition of certain antibiotics, e.g., penicillin, aureomycin, terramycin, 

 and streptomycin, to the ration will increase the rate of growth of animals 

 usually 10-20 per cent, even under farm conditions. The quantity fed 

 is small (2-5 mg. per pound of feed). It is thought that the antibiotics 

 inhibit the growth of those organisms which assimilate large quantities 

 of certain vitamins present in the intestinal tract and which therefore 

 reduce the supply for absorption by the animal. 



* 



REVIEW QUESTIONS ON DIGESTION 



1. Discuss the digestion of (1) proteins, (2) starch, (3) fat. 



2. Define (1) conditioned reflex, (2) chyme, (3) secretin. 



3. Which reactions are catalyzed by the following enzymes: (1) pepsin, (2) rennin, 

 (3) ptyalin, (4) lipase, (5) carboxypeptidase, (6) amino peptidase, (7) nucleotidases? 



4. Persons with obstructed bile ducts hemorrhage easily, even when their diets con- 

 tain large quantities of vitamin K. What may be the reason for this condition? 



REFERENCES AND SUGGESTED READINGS 



Best, C. H. and Taylor, N. B., Physiological Basis of Medical Practice, Williams and 

 Wilkins Company, Baltimore, 1950. 



Elvehjem, C. A., "Nutritional Significance of the Intestinal Flora," Federation Pro- 

 ceedings, 7, 410 (1948). 



Grossman, M. I., "Gastrointestinal Hormones," Physiol. Rev., 30, 33 (1950). 



Hawk, P. B., Oser, B. L., and Summerson, W. H., Practical Physiological Chemistry, 

 12th ed., The Blakiston Company, Philadelphia, 1947. 



Northrop, J. H., Kunitz, M., and Herriot, R. M., Crystalline Enzymes, Columbia 

 University Press, New York, 1948. 



