The gastro-intestinal tract converts starches into glucose, inverts sucrose into glucose and fructose, and lactose into glucose and galactose, so that these soluble mono-saccharids become the fuels transported by the blood for the nourishment of the body-cells. The enzymes maltase, invertin, and lactase which, respectively, convert maltose, suchrose, and lactose into monosaccharids, are present in the intestinal mucosa of the newborn infant.1

The writer personally prepared fructose from inulin in 1889, which when given to a fasting rabbit caused the formation in its liver of large quantities of glycogen, the anhy-drid of glucose.2 To a lesser extent the same fate may befall ingested galactose. After giving glucose or fructose, as much as 40 per cent, of the dry solids of the liver consisted of glycogen. These monosaccharids were not changed in the intestine.

1 Ibrahim: "Zeitschrift fur physiologische Chemie," 1910, lxvi, 19. 2Voit: "Zeitschrift fur Biologie," 1891, xxviii, 245.

Isaac1 perfused a fluid made up of washed dog's blood-cells and Ringer's solution containing fructose through the liver of a fasting dog and found that the fructose was converted into glucose. The change in the composition of the perfusing fluid was as seen below:

Before Perfusion.

Three Hours Later.

d-Glucose........

..... 0.012 per cent.

0.310 per cent.

d-Fructose.......

..... 0.349 "

0.020 "

Ishimori2 has reported that glycogen deposition in the liver follows the intravenous injection of glucose and fructose in the rabbit, although galactose does not have this effect. Galactose is less readily oxidized, at least in the adult organism, than are the other two hexoses (see p. 294), though it may be that the conditions for its breakdown are more favorable in the suckling.

The quantity of glycogen present in a living animal cannot be accurately estimated. Schondorff3 gave seven dogs diets rich in carbohydrate for several days, and found that the quantity of glycogen present in their bodies varied between 7.59 and 37.87 grams per kilogram.

The distribution of this glycogen in 100 grams of the fresh tissue varied as follows:

Maximum.

Minimum.

Liver ........................

18.69

7.3

Muscle ...................

3.72

0.72

Heart................................

1.32

0.104

Bone.................................

1.90

0.197

Intestines ....................

1.84

0.026

Skin

1.68

0.09

Brain................................

0.29

0.047

Blood................................

0.0066

0.0016

The traditional distribution of glycogen, one-half to the liver and one-half to the rest of the body, Schondorff shows to be incorrect. For 100 grams of liver glycogen there occurred in the rest of the body the following amounts:

1 Isaac: "Zeitschrift fur physiologische Chemie," 1914, lxxxix, 78.

2 Ishimori: "Biochemische Zeitschrift," 1912-13, xlviii, 332. 3Schondorff: "Pfluger's Archiv," 1903, xcix, 191.

Dog

I........................................

398 grams.

II.........................................

279 "

"

III........................................

87 "

"

IV........................................

76 "

"

V........................................

159 "

"

VI........................................

355 "

"

VII........................................

105 "

It is an interesting observation of Kulz1 and of Jensen2 that an active organ like the heart maintains its normal glycogen content even after fifteen days of starvation.

In the various discussions on the subject of glycogen it has been shown that in starvation, and after protein and sugar ingestion, there is glycogen present in the body - a constant supply always ready for emergencies, which can be reduced through exercise, but which is only to be completely removed by tetanic convulsions (pp. 107 and 457).

The writer has here avoided the discussion of a production of sugar from fat. To his mind the evidence is against such production, as will be demonstrated in the chapter on Diabetes.