Galen's Commentaries on the Aphorisms of Hippocrates

is held to be refined in children. Just as it happens that one finds many of those who are in the prime of life possessing a biting heat, which is no longer moist and vaporous, nor airy. Nor should this seem a wonder. For it is necessary that the outflow be similar to the underlying substance, so that when a moist and airy substance exists, then that which flows from it is vaporous and gentle. But when the substance is earthy and dry, then that which flows out is also smoky, sooty, and acrid, which also occurs in external things. For those things which evaporate from sweet and warm water are excellent and vaporous, but those which come from some burnt solid body are smoky and acrid.

Since, therefore, there are two substances, and the one indeed possesses a gentle heat, while the other possesses a harsh one, children have a great deal of the former, but those in the prime of life have the latter, namely in proportion to the whole body. So that the discourse may be more natural, by transferring the whole matter to the elements, I shall proceed in this manner: Since there are four elements from which all bodies are tempered, a child's body contains within itself much airy and watery substance, and very little earthy. On the contrary, the bodies of those in the prime of life derive from earthy dryness, while watery and airy substance is lacking. Thus, even if we were to suppose the fourth element—namely fire—in equal portion in both, and should wish the bodies to be equally hot, we would nonetheless not say that the hot substance is similar in both, since the substance of children is moist, while that of those in the prime of life is dry.

For the moist is especially akin to innate heat, because our generation is from the moist. But the dry is proper to adventitious heat. Thus, newborn infants, participating in a great deal of hot, watery, and airy substance, would be said to have the most innate heat. But those who are in the vigor of life, and those already declining, insofar as those elements are lacking and the earthy superabounds, would themselves be thought to have so much less of the substance of native heat.

I think no one doubts that it is necessary that more should flow out from a watery and airy substance than from an earthy one, even if both are equally hot according to quality. This you may clearly observe even in external things. For from bodies that reach a similar heat, an equal portion does not seem to flow out; rather, from dry ones the least, and from moist ones the most. Immediately, therefore, when water and oil are moderately heated, a great deal flows out and is dissolved; but from iron, bronze, and stones, very little. So much so that if it should please you to expose water to the burning sun, if it should so happen, and iron of equal weight, and then, the day having passed, to weigh both, you will find the water rendered much less than itself, but the iron equal. Thus also if you wish to compare oil to bronze, iron, and stone, you will find the former consumed, but the latter retaining an equal mass of substance. From here you may pass on to wax, pitch, bitumen, and resin, and whatever other things possess much moist substance; you will see that these also are much more consumed and flow away under the hot sun than stone, bronze, iron, and other very dry things.

Wherefore, if nourishment is necessary so that what has flowed out from the body may be replenished, and much more flows out from the moister things and those participating more in air, it follows that bodies of this kind have need of more nourishment. The body of children is of such a kind, possessing more moist and airy substance, and not, like those of youths, the declining, and the old, possessing dry and earthy substance. Hippocrates, therefore, since he had proposed in this book to deliver a compendious and aphoristic teaching, did not expand the discourse as I have now; but in place of those words—"Those which grow bodies, even if they have an equal hot and fiery substance with those who are in the prime of life, yet those which grow have more of watery and airy substance"—he said: "They have the most [innate heat]..."