Observations (Patterson) were made on the bullfrog (Rana caterbiana) and the common snapping turtle (chelydra serpentina) by the balloon and the balloon X-ray method. In the turtles the balloon was introduced through an ordinary gastrostomy opening. In the frogs a stomatotomy was made by a small incision between the ramus of the inferior maxillary and the anterior coronary of the hyoid bone through the skin, the mylo-hyoid muscle, and the mucous membrane of the throat.
There are slight, if any, tonus variations in the empty stomach of frogs and turtles. In healthy frogs the stomach exhibits continuous rhythmical contractions. These contractions are remarkably strong, sustaining a column 15 to 22 cm. high. The contraction phase is abrupt; the relaxation is slower; in fact, it proceeds until the next contraction. The X-ray studies in the intact animal as well as observations on the isolated stomach showed that each contraction is a peristaltic wave starting at or near the cardia and sweeping over the entire stomach, just as is the case with the gastric hunger contraction in the mammals. The striking difference between the bullfrog and the mammal is the absence of periodicity or grouping of the frog's gastric contractions (Fig. 8, a).
The amplitude of these contractions in the frog is increased during prolonged starvation, but there is no obvious increase in tonus. The contractions cease at temperatures above 380 C. and below 130 C. It is significant that the cessation of the hunger contractions of the empty stomach at low temperature (i3°C.) is not in tonus, but in atpny of the stomach. It would thus seem the gastric hunger mechanism is paralyzed in the hibernating frog.
The hunger contractions of the empty stomach of the turtle are very similar to those of the bullfrog. The rate of the contraction is somewhat less, and there are periods of relative quiescence of the empty stomach similar to that in mammals and birds. In prolonged starvation the contractions become stronger and show a tendency to pass into short periods of incomplete tetanus (Fig. 8, b).