566 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



canal, especially in herbivore (see p. 532). and owing to the production of fatty acids it may 

 have value as a food. In man only young and tender cellulose is digested, such as occurs 

 in lettuce and celery. The bulk of herbivorous fecal matter consists of cellulose. Cellulose 

 is only with difficulty attacked by acids and alkalies. Tunicin, found among the tunicates, 

 is identical with cellulose, so that the substance is not solely characteristic of the vegetable 

 kingdom. 



Starch, (C 6 H 10 O 5 ) 20 . — This substance on boiling with dilute acids breaks 

 down by hydrolysis principally to dextrose. It is found in plants, and 

 may be manufactured by them from cane-sugar, dextrose, levulose, and from 

 other sugars. It forms a reserve food-stuff, being converted into sugar as the 

 plant requires it — in winter, for example. Starch gives a blue color with 

 iodine. According to recent investigations 1 starch is said to be broken up by 

 diastase into five successive hydrolytic cleavage-products as follows : (1) Amylo- 

 dextriu ( ( 'jdlajO,^, a substance giving a deep-blue color with iodine. This 

 is next changed to (2) Erythrodextrin, (C 12 H 2() Oi ) lg + H 2 0, or (C^H^O^)^. 

 (( '^.HjjO,,), which is readily soluble in water and gives with iodine a reddish- 

 brown color. Erythrodextrin is converted into (3) Achroodextrin, (C 12 H 20 O 1() ) 6 

 + H 2 0, or (C^H^Oio^.C^H^On, which is likewise very soluble, tastes slightly 

 sweet, but gives no coloration with iodine. Achroodextrin now breaks up 

 into (4) Isomaltose, which through change in configuration is transformed to its 

 isomere (5) Maltose. 



Products similar to these are formed by the various diastatic ferments in 

 the body, and in addition also some dextrose. Ptyalin 2 acts rapidly on starch, 

 producing dextrin and maltose, butvery little dextrose. Amylopsin, from the 

 pancreas, acts still more rapidly than ptyalin, and with the production of con- 

 siderable dextrose. The diastatic ferment of intestinal juice acts very slowly 

 on starch, forming dextrin, maltose, and a little dextrose, while the ferment in 

 blood-serum likewise acts slowly but with complete transformation of all the 

 maltose and dextrin formed, into dextrose. 



The above facts lead Hamburger to suggest that the diastatic ferments of the body 

 consist of mixtures, in different proportions, of diastase, which firms dextrin and maltose 

 from starch, and of glucase, which converts these into dextrose. This, however, is merely 

 an hypothesis, and glucase has never been prepared. The vegetable diastase is not iden- 

 tical with that found in the body. Tims ptyalin, like cmulsin. breaks up salicin into sali- 

 cylic alcohol and dextrose, of which action vegetable diastase is incapable. But ptyalin, 

 again, is not identical with emulsin, for it will not act on amygdalin. 



The subcutaneous injection of solutions of achroodextrin, erythrodextrin, anil amylo- 

 dextrin results in their partial elimination in the urine, the rest being burned. 3 



Glycogen, or Animal Starch.— Recent investigations have shown that in 

 all the particulars of diastatic decomposition glycogen is identical with vege- 

 table starch. 4 Glycogen is soluble in water, giving an opalescent fluid. The 

 blood has a normal composition which does not greatly vary. After a hearty 

 meal excess of fat is deposited iu fatty tissue, excess of proteid in the muscular 



1 Lintner und Dull : Berichte der dt »/.«•/,< » cIk nu.-rlien Gesellschaft, 1893, Bd. 26, S. 2533. 



2 See Hamburger: Pfluga'i Arckiv, 1895, Bd. 60, S. 573. 



8 Yoit, )■'. Deutsche* Archivfiir klinische Median, Bd. -13. S. 523. 

 4 Kiil/. and Vogel : Zetochrift fur Biologie, Is'.'."), Bd. 31, S. 108. 



