Chinese Journal of Physiology

BASAL SECRETION OF THE STOMACH 53

(e.g., action of secretagogues in meals). With direct stimulation, the secretory response is an increase by a fixed proportion according to the level of the basal secretion, viz., y=k-+a, where y is the response, ka constant and x the basal secretion. With indirect or meal stimulation the response cannot, as we have just seen, be predicted in this way. The reason for the difference must therefore be in the variability of the stimulating mechanism intervening between the indirect stimulant or secretagogue and the gastric cells.

Variability of the intermediary mechanism, however, may be complicated by alterations in the excitability or threshold of the secreting cells. We know for example that immediately after denervation (10) or following an injection of histamine (8) the threshold of the gastric cells is raised. It is possible that the converse, i.e., a lowered threshold may occur. In fact repeated subminimal stimulation appears to lower the gastric threshold (6), . Variations in the threshold or excitability of the secreting cells may well be termed tone, but at the moment only conditions of depressed tone are known unless the clinical condition of hypersecretion is an example of increased excitability. The observations with histamine show that the tone of the glands is relatively constant under approximately standard conditions but do not exclude the possibility of increased tone under other yet physiological conditions. A raised secretory tone would permit stimulating factors (nervous or chemical) present in subliminal degree to act on the secreting cells, but tone does not in itself explain the basal secretion, Lastly tone must not be confused with reactivity, the former indicates the ability of the cell itself to respond to direct stimulation, while the latter indicates the ability of the entire gastric secretory apparatus (viz., receptive surface, intermediate mechanism and cell) to respond to indirect (meal) stimulation. Complete atony would prevent reactivity, but a non-reactive stomach might still respond to direct stimulation.

The present experiments show that secretion still occurs under basal conditions, although much limited in range, after all extrinsic nerves are divided. This reduced secretion must therefore be due either to the activity of the loca] enteric elements of the pouch or to chemical factors. Chemical excitants have been recovered from the circulation (13) under basal conditions and on occasions in amounts sufficient to account for a high basal secretion. Now these excitants must arise from either the stomach or intestine. We know that marked and even absolute delay of the total food residues in the smal] intestine