upon it strips of adhesive paper. Instead of attempting to weigh the covering itself, the "model" of the body was cut up into pieces which would lie out flat so that its area could be determined by photographing it upon sensitive paper. The total area was then found by weighing the photographic silhouettes and comparing with

FIG. 199.-A Cretin, Benny L., and his surface mold. (Du Bois, Archives of Int. Med. Chicago, 1915, XV, 872.)

the weight of a unit area of the same sensitive paper. The areas of the several members of the body as measured were then compared with the areas as given by multiplying their lengths by sums of measurements representing circumferences. For example, the area of the arm was given by multiplying the length from the outer end of the clavicle to lower border of radius F, by the sum of the three circumferences at: Upper border of axilla G; largest girth of forearm H; smallest girth of wrist I. This calculated area compared with the actual area for several individuals gave a factor which, used with the product just given, made up a so-called linear formula for the arm; thus: FX (G+ HI X 0.558. The several subformulæ added together could then be employed for measuring the surface of the entire body.

This method resembles the one proposed by Roussy 153 in which the surface was given by multiplying the mean perimeter pm by the mean peripheral total height (Hm); thus S = Pm × Hm. The first factor was found by taking the mean of 29 different circumferences (Fig. 200), while Hm is the sum of the three partial heights: (a) head, neck and shoulders; (b) trunk and lower extremities; and (c) upper extremities.

From his measurements Meeh derived a formula based upon the well-known relationship of surface to mass of similar solids; namely, that the former varies as the two-thirds power of the latter. By employing a constant, 12.3, Meeh found that the formula S = Vw2 gave results within seven per cent. of those determined by actual measurement. DuBois found an agreement between measured and calculated values for five cases within two per cent. Later50 the measurements were greatly simplified and a formula containing total height, weight and certain constant factors was devised. This is known as the heightweight formula, A W0.425 X H0.725 X C, where A is surface in square cemtimeters, H the height in centimeters and W the weight in kilograms. C is a constant 71.84.

=

=

Hm is

(Hm): s FIG. 200.-The surface of a man's skin is equal to the product of his mean perimeter (Pm) by his peripheral mean total height Pm X Hm. Pm is obtained as the mean of 29 different circumferences including the slimmest and most robust. the sum of the three mean partial heights: a, head, neck and shoulders; b, trunk and lower extremities; c, upper extremities. (After Roussy. Compt. Rend. l'Academie de Sciences, July 17, 1911-T153, p. 206, both figures.)

12.

13

....12'
....13'

D

Further discussion of the surface areas of infants will be found in later sections (pages 600, 640).

Protection Against Heat Loss.-Practically all warm-blooded animals have some means of protection against excessive heat loss. The most important of these are the natural coverings (hair, fur, feathers) on the skin and subcutaneous fat. The chief value of hair, fur, etc., in this connection lies in the large quantity of stagnant air which they occlude. This air, being stagnant, retards the conduction of heat away from the body. Subcutaneous fat, on the other hand, is a poor conductor of heat, a layer only 3 mm. thick having been found to diminish the heat loss in a unit of time more than 50 per cent. Subcutaneous fat is especially important for aquatic mammals, because the water wets the fur, driving out all the air.

The human body, not being provided with a complete natural coat of hair, requires the aid of artificial coverings in order to maintain its temperature in climates which average less than 27 or 28°C. Above this temperature, the naked body is able to regulate its temperature unaided. Clothes serve to diminish the movement of warm air away from the body, in the same way as hair, fur, and feathers do. It has been estimated that no less than 10 liters may be occluded by the meshes of a woolen suit of clothes, and some 10 to 20 liters more may be held in the spaces between different garments and between the garments and the body. Heat loss by radiation is also reduced by clothes, the exact effect depending on the conductivity of the material. importance of artificial covering for the infant, whose heat-regulating mechanisms are not yet functional to their full capacity is at once apparent, especially in view of the enormously greater surface in proportion to weight of the infant's body (see discussion at p. 642).

The

Regulation of the Body Temperature. It has been noted above (p. 524) that the body temperature varies between very narrow limits. This fact, in itself, is a proof that the mechanism of heat production is very nicely adjusted to the process of heat loss. How is this coöperation brought about? It has been shown that, when a man is subjected to an external temperature (bath) varying slowly between 34 and 37°C., the mechanism of heat loss (sweating) is brought into play when the body temperature (rectum) is raised on the average 0.34° and the mechanism of heat production (shivering) when the body temperature has fallen on the average 0.26°. Likewise, in muscular work, sweat breaks out when the body temperature has been raised on the average 0.43°. Whether the reaction in each case is brought about by the change in temperature of the blood and the direct stimulation of the sweat centers or the motor centers respectively, or by reflex stimulation of these centers through the cutaneous nerves, is not definitely known. There is much evidence that the corpora striata in the base of the forebrain contain a center which is particularly susceptible to changes in temperature and to mechanical stimulation, 105, 192

Influence of Food on the Heat Production.-The observation of Lavoisier that the heat production was increased by taking food was

confirmed by Pettenkofer and Voit, who found that the total metabolism of a dog was increased from 34.9 to 65 calories per kilogram as the result of eating about two and one-half pounds of meat. Feeding fat they observed no increase in the heat production unless the amount fed was far in excess of the body requirements. Feeding carbohydrate in the form of starch, they found that 3.79 gm. in the food increased the metabolism 17 per cent. over that of the starving animal. More exact information concerning the influence of carbohydrate came with the invention of methods by Zuntz and by Benedict by which the oxygen absorption could be determined, since, without this knowledge, it was impossible to distinguish the part taken by fat in the total heat production from that taken by carbohydrates. Magnus-Levy using the Zuntz method with human subjects, came to the conclusion, substantially in accord with those of Pettenkofer and Voit, namely, that moderate quantities of fat do not increase the heat production (absorption of oxygen), but that both carbohydrate and protein increase it considerably. Rubner, using only the excretion of CO2 as the measure of heat production, formulated laws regarding the influence of different foods given to dogs, as follows: Since the different foodstuffs affect the heat production to a different degree, we may speak of their "specific dynamic action." The proper basis of comparison is the amount of heat produced by the fasting animal. Taking this quantity as the minimal requirement of the animal for energy (in potential form), and feeding this quantity in the form of different foodstuffs, the effect is for protein an increase in heat production of 30 per cent., for fat 11 per cent., for carbohydrate 5.8 per cent. In order to keep the animal in an energy equilibrium, therefore, it is necessary to feed him in protein 140 per cent. of the requirement, in fat 114 per cent., and in carbohydrate 106 per cent. 105

Lusk 207 and his co-workers, using a small respiration calorimeter of the Atwater-Rosa-Benedict type suitable for studies on dogs, babies, or dwarfs, have demonstrated that the increased heat production after ingestion of proteins is due to the amino-acids into which the protein is broken up by digestion. It is, however, not the mere absorption of the amino-acids themselves, nor their direct oxidation which accelerates the metabolism, but the stimulating effect of the intermediate oxyacids which are formed from them. Quantitatively the results of these more modern researches confirm the conclusions of Rubner as to the specific dynamic effect of protein. These, however, relate to the dog. In man the dynamic effect is ordinarily not so great. The dynamic effect of protein in milk upon the metabolism of the infant will be discussed later (p. 634 seq). It need only be added here that protein which becomes a part of the body does not affect the heat production.

The dynamic effect of fat, it turns out, is not so high as Rubner found it, if reckoned for the entire day, but for individual periods. up to six hours after feeding, 127 may increase the metabolism as much as 30 per cent., as contrasted with protein (meat) which may raise

VOL. I-35

it to 42 per cent. Bloor 30 found that the fat in the blood also may increase up to six hours after feeding.

Following Rubner's fundamental observation on the influence of carbohydrate on the respiratory metabolism of a fasting dog, Magnus-Levy, Johansson, Dürig, and DuBois, made confirmatory

FIG. 201.-Heat production of a dog after giving: a, fat; b, glucose after fat; c, glucose and fat; showing summation. (Murlin and Lusk, Journ. of Biol. Chem., 1915, XXII, Chart I, p. 18.)

observations on the human subject. One hundred grams of glucose causes an average increase of nine per cent. in the heat production of a man of 75 kg.; and 200 gm., one of 12.5 per cent. during three to six hours after the ingestion.63 The same dose with a smaller man produces a proportionally greater acceleration of the metabolism.