The Irritability and Chronaxie of the Small Bowel.

Abstract

In view of Lapicque's claim that the chronaxie is one of the best measures of the excitability of a muscle we were curious to see what this “threshold of duration” is for the mammalian small intestine, and if it is graded from duodenum to ileum. Unfortunately, in the time that I could give to the problem no conclusion could be reached except that with both galvanic and faradic tetanic stimuli the time required in order to get a response varied between 0.1 and 0.6 second. In 3 animals the chronaxie appeared to be graded downward with short intervals in the duodenum and long ones in the ileum, and in one there was no gradation. The problem will have to be studied further probably with a different type of apparatus. I used the electrodes and technic described by Alvarez and Hosoi. 1 The duration of current flow was determined by 2 keys which were opened either by a Lucas pendulum 2 or by a gravity operated arm, the descent of which was regulated by a dash-pot. The Lucas pendulum with the keys separated as widely as possible delimited an interval which usually was too short for effective stimulation.

With such a long chronaxie as was found it is curious that the neuromuscular wall of the bowel should respond at all to the rapidly interrupted faradic current.

During the course of these experiments it was necessary to measure the threshold for faradic stimulation and the opportunity arose of checking the recently published observations of Alvarez and Hosoi. Fig. 1 shows that a gradient of irritability similar to the one described by them was found in 1.2 out of 17 rabbits. In 2 the irritability was low and about the same in all parts of the bowel, and in 3 the gradation was irregular.