SPECIAL CONSTITUENTS OF THE DIET. 881 



be prevented, as by tying the ureters, the excess of sugar under- 

 goes changes which result in the formation of lactic acid, acetone, 

 diacetic acid, and other substances, the production of which is 

 accompanied by convulsions, and eventually coma, as in severe natural 

 diabetes. 1 



Very large amounts of starch can be taken into the alimentary canal, 

 and corresponding amounts of dextrose absorbed into the blood, without 

 producing glycosuria in a normal animal. But if the assimilation 

 powers have been reduced by starvation, glycosuria is found to occur on 

 the ingestion of a large amount of starch. 2 On the other hand, if cane- 

 sugar, maltose or lactose, and even laevulose, are taken by the mouth in 

 large quantities, even without a previous starvation period, part of the 

 sugar ingested appears in the urine (alimentary glycosuria). 3 This is 

 apparently due to the fact that the blood vessels of the intestine cannot 

 carry away all the absorbed sugar with sufficient rapidity to the liver, 

 and some of it consequently passes to the general circulation by way of 

 the thoracic duct, 4 and thus to the kidneys, which always immediately 

 eliminate any excess of sugar in the blood passing through them. 

 G-lycosuria also occurs when sugar solutions are injected into the large 

 intestine of dogs. 5 



Cellulose is not readily digested by carnivora nor by man, but in 

 some forms of food (carrots, cabbage, celery, lettuce) a considerable 

 proportion of the cellulose present may become dissolved and absorbed ; 6 

 in herbivora it undergoes digestion, and is eventually absorbed as 

 dextrose. Its chief value in the diet of animals seems, however, to 

 be due to its action in promoting peristalsis of the intestines. Eabbits 

 die from inflammation of the intestines if devoid of cellulose ; its place can 

 be supplied in them by horn-shavings, which have the same mechanical 

 effect. In carnivora and man this is not so important, as the gut is 

 shorter, but probably the cellulose of mixed food tends to prevent 

 constipation. A purely milk diet is well known to be constipating 

 (Bunge). 



The fate of the carbohydrates after assimilation will be treated of in 

 a special section on carbohydrate metabolism. 



Fats are taken in largely in the form of animal fat (fats of flesh and 

 milk), but also largely, especially in some countries, in the form of 

 vegetable fats, such as olive oil and the fats met with in certain seeds. 

 In the last-named form they are protected by cellulose, and are far less 

 easily digested and assimilated. The changes which they undergo in 

 the processes of digestion and absorption have already been fully con- 

 sidered (pp. 443-463), also their caloric value, and their importance as 

 proteid-sparers. Their assimilation to the natural fat of the body, and 

 their formation within the body, will be treated of subsequently. 



Fatty acids and soaps have been shown by I. Munk (in dogs) to 

 have very nearly the same nutritive value as the fats from which they 



1 V. Harley, Arch. f. PhysioL, Leipzig, 1893, Suppl., S. 46. 



2 Hofmeister, Arch. f. exper. Path. u. PharmakoL, Leipzig, 1889, Bd. xxv. S. 240 ; and 

 1890, Bd. xxvi. S. 355. 



3 Worm-Miiller, Arch. f. d. ges. PhysioL, Bonn, 1884, Bd. xxxiv. S. 576 ; Hofmeister, 

 Arch.f. exper. Path. u. PharmakoL, Leipzig, 1889, Bd. xxv. S. 240 ; C. Voit, Ztschr.f. BioL, 

 Miinchen, 1892, Bd. xxviii. S. 265 ; Miura, ibid., 1896, Bd. xxxii. S. 281. 



4 Ginsberg, Arch.f. d. ges. PhysioL, Bonn, 1889, Bd. xliv. S. 306. 



5 Eichhorst, ibid., 1871, Bd. iv. S. 601. 



6 Weiske, Ztschr. f. BioL, Miinchen, 1870, Bd. vi. S. 456 ; Knierem, ibid,, 1885, Bd. 

 xxi. S. 67. See also Luntz, Arch.f. d. ges. PhysioL, Bonn, 1891, Bd. xlix. S. 477. 



VOL. I. 56 



