Voit, when he wrote his "Physiologie des gesammt Stoff-wechsels und der Ernahrung," in 1881, was unable to give definite proofs of the conversion of carbohydrate into fat in the organism, although such conversion was popularly believed to take place. Definite proof of the conversion of carbohydrates into fat was afforded by Meissl and Strohmer,1 who gave a pig, weighing 140 kilos, 2 kilograms of rice containing 1592 grams of starch daily for seven days, and collected the carbon and nitrogen of the excreta by means of a Pettenkofer-Voit apparatus during two days of the period. The average results per day were as follows:

The nitrogen retained represented 38 grams of protein containing 20.1 grams of carbon; 269.12 grams of retained carbon were therefore available for glycogen or fat construction. Since the amount of carbon retained exceeded the possible glycogen formation, fat must, therefore, have been added to the body. Had all the carbon retained been converted into fat it would represent a production of 343.9 grams of fat. Of this only 33.6 grams of fat could have arisen from the protein metabolism of the period. Hence it is possible that 310.3 grams of fat may have originated from 1592 grams of starch ingested, which indicates a conversion of 19.5 per cent, of the starch given into fat.

Similar experiments were made with geese by E. Voit and C. Lehmann.1 The geese were starved four and a half days and were then fed with rice.

1 Meissl and Strohmer: "Sitzungsberichte der k. Akad. d. Wissenschaften," 1883, lxxxviii, III Abtheilung.

One of these respiration experiments which lasted thirteen days has been published,2 and is as follows:

At the commencement of the experiment the animal weighed 4 kilograms. There was no protein retention, but 31 per cent, of the carbon ingested was not eliminated. The protein metabolism could not yield nearly enough carbon to account for that retained. As the rice contained but 0.51 per cent, of ether extract, the retained carbon could not have been administered in the form of fat. If 367.3 grams of carbon had been retained in the form of glycogen this would have aggregated 851 grams, or 20 per cent, of the whole goose, or the starch content of a potato. This is a manifest impossibility, since E. Voit3 found only 2.2 per cent, of glycogen in a goose which had been largely fed on rice. Since the carbon retained could not have been stored as glycogen, the only alternative remaining is to assume its retention as fat.

Rubner about the same time showed the same principles to be true in the case of the dog.

It is evident, then, that pigs, geese, and dogs can convert carbohydrates into fat. The fattening of cattle may be similarly accomplished.

The ability to convert carbohydrate into fat probably exists throughout the animal kingdom. Thus Weinland4 has expressed from living ascaris ferments which convert glycogen into glucose and then into valerianic and possibly caproic acids - 0.8 gram of dextrose yields 0.3 gram of valerianic acid.

1 Voit: "Sitzungsberichte der kgl. bayr. Akad. d. Wissenschaft," 1885, p. 288.

2 Lehmann and E. Voit: "Zeitschrift fur Biologie," 1901, xlii, 644. 3E. Voit: Ibid., 1889, xxv, 543.

4 Weinland: Ibid., 1901, xlii, 55; 1902, xliii, 86; 1904, xlv, 113.

This is suggestive of a wide-spread biologic capability.

When carbohydrates are converted into fat in the organism the respiratory quotient (Volume CO2/Volume O2, may rise very considerably above unity. This is for the reason that an oxygen-rich substance like glucose is being converted into substance which is poor in oxygen. Hence the volume of expired carbon dioxid may be greater than the volume of inspired oxygen. Max Bleibtreu1 found that the respiratory quotient of a goose which had been stuffed with grain was 1.33, whereas the same goose when fasting showed a normal quotient for that condition of 0.7 28. Pembrey2 describes how marmots previous to the winter hibernation instinctively devour large quantities of carbohydrate food, and how the respiratory quotient may rise even as high as 1.39. This indicates a fat production for use during the winter.

Grafe3 gave to a fasting dog three times his daily caloric requirement of energy in the form of carbohydrate, and noted an increase of 33 per cent, in the heat production and a maximal non-protein respiratory quotient of 1.31. A discussion of the intermediary chemical reactions involved in this process has already been given (see p. 268). Written in their simplest formulae the production of butyric or of palmitic acids from glucose would read:

C6H4206 + O2 = C4H8O2 + 2CO2 + 2H20 4C6H420 + O2 = C16H3202 + 8CO2 + 8H20

One may accept Bleibtreu's formula as the simplest expression of the conversion of carbohydrate into fat, as follows:

270.6 gm. glucose = 100 gm. fat + 115.45 gm. CO2+ 54.6 gm. H2O 997.2 calories = 950.0 calories.

1 Bleibtreu: "Pfluger's Archiv," 1901, Ixxxv, 345.

2 Pembrey: "Journal of Physiology," 1901, xxvii, 407.

3 Grafe: "Deutsch. Archiv fur klin. Med.," 1914, cxiii, 1.

The reaction is evidently exothermic, 4.7 per cent, of the heat being liberated. If the heat evolved be measured on the basis of the extra carbon dioxid production, 1 liter of such carbon dioxid would have a value of 0.8 calorie, or less than one-sixth the caloric equivalent of a liter of carbon dioxid obtained from the oxidation of glucose in the ordinary manner. On the basis of this the heat production of a dog after giving 70 grams of glucose was calculated in experiments performed by Lusk.1 The results of two of the three experiments are presented in the accompanying table:

Dog III. Metabolism After Giving 70 Grams Of Glucose In 210 C.C. Of Water At 38°

That the method of calculation of indirect calorimetry in the presence of respiratory quotients above unity is correct may be deduced from these experiments. The "uncorrected" heat values represent calculations based on the oxygen absorption alone, while the "corrected" values are those in which the quantity of C02 eliminated in excess of a non-protein respiratory quotient of unity is given a value of 0.803 calorie per liter.

It is evident that after a large ingestion of glucose direct and indirect calorimetry agree closely if the heat value of the carbon dioxid which is evolved in the intermediary transformation of carbohydrate into fat be taken into consideration.

1 Lusk: Loc. cit.

During the first three hours of Experiments 88, 90, and 91 the calculated heat production was 75.81, 75.30, and 75.64, while the C02 excretion in excess of a non-protein respiratory quotient of 1.00 was 1.07, 0.80, and 1.73 liters; it is, therefore, apparent that the intensity of metabolism is not related to the height of the respiratory quotient. The transformation of carbohydrate into fat takes place with the liberation of very little energy, and the height of the total metabolism is scarcely affected by the process.