"Mute and still, by night and by day, labor goes on in the workshops of life. Here an animal grows, there a plant. The wonder of the work is not less in the smallest being than in the largest."1

In the last chapter the average food requirement of a normal adult organism was discussed. This diet, however, may be exceeded in cases where there is a renewal of tissue following wasting disease, or where there is a development 'of new tissue, as during pregnancy, or afterward during lactation, which involves the growth of the newborn infant.

Tangl2 has reported some interesting observations on the heat production which takes place in the hen's egg incubated at 380 and 39° F. Tangl called this the "energy for development" or the "ontogenetic energy." His method was to determine the calories in fresh laid eggs and to compare that amount with the calories found within the egg-shell at the moment of the birth of the chick. In this latter case the chick and the balance of egg-yolk were determined separately.

The results of these experiments showed that for the development of 1 gram of chick 658 small calories were used, or for the production of 1 gram of solids contained in a newborn chick 3425 small calories were required.

Farkas3 has since shown that for the development from the egg of 1 gram of silkworm larvae 882 small calories are required, or for 1 gram of dry solids, 3125 small calories, figures which he compares with Tangl's for the egg.

1 Rubner: "Verhandlungen der Ges. der Naturforscher und Arzte," 1908, P. 77.

2 Tangl: "Pfluger's Archiv," 1903, xciii, 327. 3 Farkas: Ibid., 1903, xcviii, 490.

When the whole hen's egg is considered, Tangl finds that 32 calories or 35 per cent, of the amount of chemical energy in the original egg is deposited in the body of the young embryo. The energy of development used in the production of the young chick amounts to 16 calories or 17 per cent, of the original total. The balance, 44 calories or 48 per cent, of the original energy in the egg, is largely found in the abdomen of the chick and is absorbed by the animal during the early days of life.

It is apparent from the above that approximately one-sixth of the energy in a hen's egg is used in the development of a chick whose body contains one-third the original energy of the egg. The other half of the energy becomes available for the chick during the first days of its separate life through absorption from the intestinal wall.

Tangl finds that each egg loses in solids during incubation, and that the heat value of 1 gram of such solids is over 9 calories. Since 1 gram of fat yields 9.3 calories, the natural inference is that fat furnishes the energy for development.

Hasselbalch4 had formerly shown that the respiration carried on by an egg indicated a respiratory quotient amounting to 0.677. This low quotient points to the combustion of fat.

Tangl2 also states that there is no loss of protein nitrogen by the egg during incubation, and that the egg-shell contributes to bone formation in the chick.

Glaser3 has found that the energy of ontogenesis for the eggs of fundulus is similar in quantity to that necessary for the hen's egg and for silkworm larvae, and is also evolved at the expense of the oxidation of fat. He reiterates Tangl's statement that the specific energy of ontogenesis is not a function of phylogenetic position or of organization, but that the embryonic construction of different kinds of highly organized living forms may take place at the same expense of chemical energy.

1 Hasselbalch: "Skan. Archiv fur Physiol.," 1900, x, 353.

2 Tangl and Mituch: "Pfluger's Archiv," 1908, cxxi, 437; Tangl: Ibid., 423.

3 Glaser: "Biochemische Zeitschrift," 1912, xliv, 180.

There is no change in the intensity of the oxidation processes in women during menstruation, a fact first shown by L. Zuntz1 and confirmed by Du Bois.2

Schrader3 showed that there was a retention of protein nitrogen in six women either during the whole menstrual period or during the first part of it. This is in compensation for the loss of blood.

During pregnancy in the higher animals not only must there be growth of the breasts, of the uterine musculature, and of the embryo itself, but there must be energy expended in maintaining the new organism; hence the appetite of the mother increases during pregnancy. Magnus-Levy4 finds an increased requirement for oxygen on the part of the mother as pregnancy progresses. His table is as follows:

Rubner5 called attention to the fact that the mammalian embryo has no appreciable weight in relation to the mother until the middle of the gestation period, and, in fact, up to this time the metabolism of the mother is usually found to be unchanged.6 At term, however, the weight of the child is between 5 and 6 per cent, that of the mother, and when the various adnexa are considered the mother loses during parturition the equivalent of 20 per cent, of her postpartum weight.

1 Zuntz, L.: "Archiv fur Physiologie," 1906, p. 393.

2 Gephart and Du Bois: "Archives of Internal Medicine," 1916, xvii, 907. 3 Schrader: "Zeitschrift fur klinische Medizin," 1894, xxv, 72.

4 Magnus-Levy: "Zeitschrift fur Geburtshulfe u. Gynakologie," 1904, 116. 116. Also see Magnus-Levy: von Noorden's "Handbuch des Stoffwechsels," 1906, i, 409.

5 Rubner: "Archiv fur Hygiene," 1908, lxvi, 177.

6 Zuntz: "Ergebnisse der Physiologie," 1908, vii, 430; "Archiv fur Gynakologie," 1910, xc, 452.