. A text-book of physiology : for medical students and physicians . h pepsin; then, as it is slowly moved into the pre-pyloric region, the acid constituent is added. The pyloric glandsare said (Heidenhain) to secrete an alkaline liquid containingpepsin, and, according to Edkins and Starling, they form a sub-stance which is capable of acting as a chemical excitant to the * See Haane, Archiv f. Anatomie, 1905, 1. f Grutzner, Archiv f. die gesammte Physiologie, 106, 463, 1905. 768 DIGESTION AND ABSORPTION IN THE STOMACH. 769 glands secreting the gastric juice (gastric secretin or gastric hor-mone
. A text-book of physiology : for medical students and physicians . h pepsin; then, as it is slowly moved into the pre-pyloric region, the acid constituent is added. The pyloric glandsare said (Heidenhain) to secrete an alkaline liquid containingpepsin, and, according to Edkins and Starling, they form a sub-stance which is capable of acting as a chemical excitant to the * See Haane, Archiv f. Anatomie, 1905, 1. f Grutzner, Archiv f. die gesammte Physiologie, 106, 463, 1905. 768 DIGESTION AND ABSORPTION IN THE STOMACH. 769 glands secreting the gastric juice (gastric secretin or gastric hor-mone).* Histological Changes in the Gastric Glands during Secretion.— The cells of the gastric glands, especially the so-called central cells,show distinct changes as the result of prolonged activity. Uponpreserved specimens, taken from dogs fed at intervals of twenty-four hours, Heidenhain found that in the fasting condition thecentral cells were large and clear, that during the first six hours ofdigestion the central cells as well as the border cells increased in. Fig. 293.—Glands of the fundus (dog): A and A1, during hunger, resting condition;B, during the first stage of digestion; C and D, the second stage of digestion, showingthe diminution in the size of the chief or central cells.—(After Heidenhain.) size, but that in a second period, extending from the sixth to thefifteenth hour, the central cells became gradually smaller, whilethe parietal cells remained large or even increased in size. Afterthe fifteenth hour the central cells increased in size, graduallypassing back to the fasting condition (see Fig. 293). Langleyf has succeeded in following the changes in a more satis-factory way by observations made directly upon the living gland. * See Starling, Physiology of Secretion, Chicago, 1906, and Edkins,Journal of Physiology, 1906, xxxiv., Journal of Physiology, 3, 269, 1880. 49 770 PHYSIOLOGY OF DIGESTION AND SECRETION. He finds that the central cells in the fast
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