A text-book of human physiology / by Dr. Robert Tigerstedt ... tr. from the 3d German ed. and edited by John R. Murlin ... with an introduction to the English ed., by Professor Graham Lusk.

  • Tigerstedt, Robert, 1853-1923.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of human physiology / by Dr. Robert Tigerstedt ... tr. from the 3d German ed. and edited by John R. Murlin ... with an introduction to the English ed., by Professor Graham Lusk. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    servation of energy is true for the body, the heat value of these substances as determined by the calorimeter must be their heat value in the body. Quite otherwise is it with proteid. The end products of its metabolism are not all completely oxidized, and hence contain not a little potential energy. To obtain the heat value of proteid for the body we must therefore deduct from its calorimetric heat value the heat value of the waste products resulting from its metabolism. This Rubner has done in the following way. He fed a small dog with a proteid material whose calorific energy had been previously determined by combustion, and then determined the calorific energy of the corresponding urine and fgeces. The former for 1 gram of proteid decomposed was 1.0945 Cal.; the latter, also for 1 g. of proteid, was 0.1854 Cal. Finally, he deducted 0.05 Cal. for the hydrolytic absorption on the part of the proteid while in the body and for the solution of urea. For 1 g. of dry proteid we would have therefore a physiological heat value of 5.754-(1.0945 +0.1854+ 0.05)= 4.424 Cal. In an analogous way the net physiological heat value of muscle deprived of its fat only was found to be 4.001 Cal., and that of the proteid of the body destroyed in fasting 3.842 Cal. For every gram of N found in the excreta after feeding the fonner we should estimate, therefore, 25.98 (6.25 X 4.001) Cal. and in fasting 24.94 (6.25 X 3.84) Cal. Human urine yields on the average 8.0 Cal. for every gram of nitrogen con- tained. Human faeces, per 1 g. of X, yield all the way from 66 to 159 Cal., but per gram of organic substance the fairly constant value of 5.2-7.7 (mean 6.5) Cal. (Rubner, Atwater, Loewy). In most metabolism experiments one has to deal not with pure lean meat, pure starch, or a definite kind of fat, but with a mixture of various fats, carbohydrates, etc. One must be content with the determination by direct analysis of the quantity of total proteid, total fat and total carbohydrate; for absolutely exact analysis of separate kinds of proteid, etc., would make all metabolism experiments impracticable. From such determinations as those above mentioned, Ruljner calculated the mean dynamic value of the chief groups of the organic foodstuffs to be as follows: 1 g. proteid 4.1 Cal. Ig.fat 9.3 1 g. carbohydrate 4.1 From the standpoint of the conservation of energy, it is to be assumed beforehand that these theoretical calorific values must be correct also for these substances when burned in the living body. In fact wc have direct experi- mental proofs of this; and precisely because these proofs verify the assumption, they are of the greatest importance for the whole subject of physiology. As long ago as 1883, Rubner showed by a long series of experiments, the details of which we cannot enter into here, that the different organic foodstuffs can replace one another in isodynamic quantities—i. e., in quantities which yield equal amounts of calorific energy. The foregoing assumption was suf- ficiently substantiated by these results alone. But Rubner carried his investi- 8