The gastric hunger mechanism is probably inherited. At any rate, the frequency and duration of the periods of gastric hunger contractions are related to the feeding habits of the individuals or the species only so far as the feeding time and food quantity are factors in the time required for emptying of the stomach, and hence for the appearance of the hunger contractions. On the other hand, the hunger mechanism determines to a certain extent the feeding habit. Animals and children probably eat as soon as the stomach is nearly empty, if food is at hand, and the greater frequency of the gastric hunger periods in the young is probably related to the more continuous feeding on the part of the young animal.
We have made observations on a number of newborn infants, with results showing that the empty stomach at birth and in the prematurely born exhibits the typical periods of tonus and hunger contractions of the adult, the only difference between infant and adult being the greater frequency of these periods in the young. In some of the infants the observations were made before their first nursing. It is thus clear that in the normal individual the gastric hunger mechanism is completed, physiologically, and is probably active some time before birth.
The recording of the gastric hunger contractions of the newborn human infant offers no great difficulties, if one uses delicate rubber balloons of 15 c.c. capacity, attached to a flexible rubber catheter of 2 mm. diameter. Most ol the infants swallowed this apparatus without difficulty and went to sleep in our arms during the observation periods. The results were always most satisfactory with the infants asleep, as that eliminated all nervous inhibitory factors, and the disturbances from body movements and from irregularities in respiration. Practically nothing can be done with the balloon method if the infant is at all restless. All of our observations were made on healthy and vigorous infants.
In human infants, periods of gastric tonus and hunger contractions arc in evidence shortly after birth and before any food has entered the stomach. These gastric hunger periods exhibit all the peculiarities of the gastric hunger contractions of the adult, except that the periods of motor quiescence of the stomach between the hunger periods arc on the whole much shorter (10 to 15 minutes). When the gastric hunger contractions become very vigorous the sleeping infant may show some restlessness, and may even wake up and cry. If the infant is awake the very vigorous hunger contractions frequently induce crying and restlessness. A tracing showing a typical hunger period in a 9-hour-old infant before first nursing is reproduced in Fig. 6. The reader's attention is called to the fact that in infants the gastric hunger periods usually end in incomplete tetanus, an index of youth and vigorous stomach.
Fig. 6.-A period of gastric hunger contractions of a nine-hour-old normal infant before first nursing.