Experiments which were carried out by Carpenter and Murlin1 present an admirable picture of metabolism under the change in conditions effected by parturition. These authors investigated the heat production of three pregnant women in the "bed calorimeter" of the Carnegie Nutrition Laboratory and followed this with similar determinations upon the same women after parturition, each woman being placed in the calorimeter several times, alone and also with her offspring. Observations were made during one to three weeks preceding parturition and during about two weeks following the event.

A summary of the results is presented in the following table:

Metabolism Before And After Parturition. The Metabolism Of The Child Was Determined By Difference

* Child cried during the experiments.

1 Carpenter and Murlin: "Archives of Internal Medicine," 1911, vii, 184.

In cases I and III the metabolism of the child alone was almost exactly equal to the decrease of the metabolism of the woman which ensued after parturition. The authors point out that during parturition the mother loses a considerable weight of material, such as liquor amnii, blood, membranes, placenta, etc., which themselves participate little or not at all in the production of heat. In the cases here cited the heat production of the newborn infant averages 2.6 times that of the mother when the calculation is based upon the calories produced per kilogram of body weight. It is probable, though not experimentally demonstrated, that the youthful, growing protoplasm in utero is also endowed with a high metabolism per kilogram of body weight. In the pregnant condition the average weight of these three women was 63 kilograms, and 33.4 calories were produced per square meter of surface. After parturition the average weight was 53 kilograms and the heat production 33.2 calories per square meter of surface. Using Meeh's formula, the average heat production of women between twenty and fifty years old, as determined by Benedict and Emmes,1 is 32.3 calories per square meter of surface. Herein lies a most remarkable confirmation of the "law of skin area" (see p. 129). Notwithstanding a sudden loss of 10 kilograms, or nearly 20 per cent, of the body weight, as well as the loss of tissues with very uneven capacities of heat production, the sum total of energy production is not altered by gestation or parturition from the common standard of mammalian metabolism as based upon the surface area.

The three mothers nursed their children throughout the days of experimentation. It appears that lactation does not increase the heat production. This is not strange, since the rearrangement of food materials in the preparation of milk depends upon hydrolytic cleavages and syntheses which involve hardly any thermal reactions, and also because it is known also that the secretory activity of a gland, such as the kidney when it eliminates urea or sodium chlorid in increased quantity, has no influence upon the total heat production of the body.

1 Benedict, F. G., and Emmes, L. E.: "Journal of Biological Chemistry," 1915, xx, 253.

The findings of Hasselbalch4 are not essentially different from those of Carpenter and Murlin.

The composition of the urine, as regards its various constituents, is scarcely changed in pregnancy. Thus, Murlin and Bailey2 found that the output of ammonia was not increased, that the relative quantity of urea decreased because of protein retention, and that the quantity of oxidized inorganic sulphur also decreased for the same reason, retention for protein synthesis. The "creatinin coefficient" fell, which the authors explain as being due to the addition of inert material to the mother's body.

On empirical grounds von Winckel3 for many years used the following diet for pregnant women with, he says, "excellent results":

This certainly seems a very low ration and one hardly compatible with furnishing the full calorific requirement. It was employed to prevent an excessive growth of the child within the uterus.

Murlin4 has made experiments on the total metabolism in pregnant dogs. From one animal a single puppy was born as the result of a first pregnancy and a litter of five from a later one. The following results were obtained:

1 Hasselbalch: "Skan. Archiv fur Physiologie," 1912, xxvii, 1.

2 Murlin and Bailey: "Archives of Internal Medicine," 1913, xii, 288.

3 von Winckel: von Leyden's "Handbuch der Ernahrungstherapie," 1904, ii, 469.

4 Murlin: Proceedings of the American Physiological Society, "American Journal of Physiology," 1909, xxiii, p. xxxii.

The increase of metabolism which can be attributed to the pregnant condition may be found by subtracting the metabolism during sexual rest from that observed just before parturition. By so doing the following figures were obtained:

First pregnancy, 551.3 - 505.3 = 46 calories daily for one puppy of 280 grams. Second pregnancy, 764.9 - 505.3 = 259.6 calories daily for five puppies of 1560 grams.

This extra metabolism was proportional to the weight of the puppies at birth. In the case of the first pregnancy the extra metabolism was 164, and in the second 165 calories per kilogram of puppy dog delivered three days later.

It is interesting to note that the mother and her five newly born puppies together produced twice as much heat as did the non-pregnant mother alone. The experiments were all made at a temperature of between 270 and 280 C. It is evident that the puppies suckled by the mother and exposed to the outside temperature had a larger metabolism than they had had in utero. For the proper maintenance of the five offspring the mother with a normal metabolism of 505 calories would have to produce milk to provide for a metabolism of about 550 calories in the puppies, and still more to furnish material for their rapid growth.

Ostertag and Zuntz1 report that a sow may yield a milk rich in fat (12.9 per cent.), and in such quantity that the energy content may amount to from two- to fivefold that required for the mother sow's metabolism.

1 Ostertag and Zuntz: "Landwirtsch. Jahrbucher," 1908, xxxvii, 226.

An extraordinary phenomenon which has been observed in dogs and rabbits is that during the early weeks of pregnancy there is a loss of nitrogen from the mother's body even when the food ingested would be entirely sufficient to maintain nitrogen equilibrium under usual circumstances.1 Jager-roos quotes Ver Ecke's description of this as "the sacrifice of the individual for the good of the species." It seems certain that the development of the fetus is accompanied by the destruction of the maternal protoplasm, perhaps, as Murlin has suggested, in order to afford hereditary building stones for the laying down of the youthful protoplasm in accordance with the type characteristic of the species.