Oppenheimer1 first called attention to the fact that the growth in grams of normal breast-fed children of the same age may be nearly proportional to the quantity of milk ingested. Here the milk presumably had the same calorific value throughout the experiment, although this could not be determined. The quantity of milk taken at each meal was found by weighing the infant before and after nursing. Oppenheimer's table is here reproduced:

Growth In Grams For 1 Kg. Milk

The proportion of growth to milk given was practically the same during the second, third, and fourth months of these children's lives.

That the growth of suckling pigs may be proportional to the calorific value of the milk has been shown by work accomplished by Dr. L. C. Sanford and Dr. Margaret B. Wilson2 in the writer's laboratory. Newborn pigs of two litters were reared on skimmed cows' milk and on the same milk fortified with 2 and 3 per cent, of glucose or of milk-sugar. The experiments were continued from fourteen to sixteen days. The results obtained in these experiments are thus tabulated:

1 Oppenheimer: "Zeitschrift fur Biologie," 1901, xlii, 147. 2Wilson: "American Journal of Physiology," 1902, viii, 197.

Growth Of Suckling Pigs

It is seen that the growth of the pigs in grams was directly proportional to the calorific value of the food to the organism. The one exception was that of an ill-nourished pig fed with skimmed milk. This was an improperly nourished animal taking too little food and remaining behind his fellows in normal development. But that 5 out of 6 pigs of different litters, of different sizes and differently fed, should have gained in weight respectively 213, 214, 215, 218, and 222 grams per thousand calories in the food ingested seems more than a coincidence.

It may be further calculated that to form 1 kilogram of body substance containing 28.7 grams of nitrogen and 866 calories requires the ingestion of 4637 calories in the food.

A pig doubles in weight in eighteen days after birth. The pig of Dr. Wilson, brought up on skimmed milk with 3 per cent, of milk-sugar added, nearly doubled in weight in sixteen days.

Comparing the fuel value of sows' milk and that of the skimmed cows' milk to which milk-sugar had been added, the following results are significant. Of 100 calories in the food there are:

It is apparent from this that normal growth of the young organism may be attained by the replacement of fat by milk-sugar in isodynamic quantity. This fact may become of importance in infant feeding.

Dr. Wilson found, when the pigs reared on these diets were killed and their composition compared with that of 3 pigs of the same litter which were killed at birth, that there was a retention for growth of 18 to 19 per cent, of the energy in the food.

In children Camerer found 15 per cent., Rubner and Heub-ner 12.2 per cent, so retained.

The percentage of calcium (CaO) in the dry solids of the pigs reared on the various skimmed milks was 8.29, 8.02, and 8.13, showing that the absorption of calcium depended on the growth of the organism, and not on a variation in the quantity ingested.

There is apparently a fixed and definite tendency toward uniform growth. Schapiro2 found that if young kittens were chloroformed twice daily their growth was retarded in comparison with normal control animals. However, on stoppage of the chloroform treatment, the greater rapidity of growth during an after period fully compensated for the earlier delay in development. (See Chapter XIII (The Nutritive Value Of Various Materials Used As Foods), p. 375).

Lusk has shown that if an amino-acid, such as alanin, be added to the diet of a dog there is a considerable stimulation of metabolism. (See p. 240.) Mendel, in unpublished experiments (cited here by permission), has demonstrated that the addition of alanin to the diet of growing rats has no influence whatever upon their rate of growth. Rubner3 set forth that the conditions which determine the "wear and tear" quota of protein metabolism and those which determine growth by the addition of a "growth quota" from protein in the diet, are entirely dissimilar, although without metabolism growth is impossible. Mendel's experiments show conclusively that the stimulation of the general metabolism itself in no way affects the fundamental capacity to grow.

1 Calculated from Ostertag and Zuntz: "Landwirtsch. Jahrbucher," 1908, xxxvii, 211.

2 Schapiro: Proceedings of the Physiological Society, "Journal of Physiology," 1905-6, xxxiii, p. xxxi.

3 Rubner: "Archiv fur Hygiene," 1908, lxvi, 43.

Another instance which demonstrates that the young organism may grow in proportion to the energy ingested in the food is brought to light by calculations based on the work of E. Rost.1 This author gave meat, fat, and bone-ash to three dogs of the same litter, the experiment starting on the ninety-eighth day of their lives and continuing eighty-eight days. The writer has thus calculated the results:

It is worthy of note that these growing dogs, fed with meat and fat, gained in weight nearly the same number of grams per 1000 calories ingested in the food. This law of growth seems reasonably established. It simply expresses the fact that during the normal development of the young of the same age and species a definite percentage of the food is retained for growth irrespective of the size of the individual.