The first few centimeters of the duodenum always beat very poorly with a small, variable amplitude. This agrees with the x-ray findings

Fig. 1. Two typical beginnings. From above downward the tracings are from duodenum, jejunum, upper ileum, lower ileum and colon. The time record represents thirty seconds.

in man where the first portion of the duodenum ordinarily remains filled and shows little activity. The food naturally is delayed in this quiet region situated between two active ones.

The greater tendency to rhythmic contraction in the upper end of the tract is suggested strongly in figure 2. The segments were first poisoned with pilocarpine and then atropin was added. The first to escape was the duodenal segment and this was followed in order by the middle, ileum and colon. A similar graded escape from inhibition has

Fig. 2. To show the graded recovery from pilocarpin after adding atropin. From above downward, the records are from duodenum, upper ileum, lower ileum and colon. Time record represents thirty seconds.

been observed with some other drugs such as adrenalin and magnesium sulfate.

The colonic segments were so slow in beginning to beat that it was found best to cut them first and to leave them in the warm solution while the other segments were being prepared. After these were fastened to the levers, they were all lowered together into the solution.

Even with this head start, the colon often took an hour to get going well and it generally beat better on the second day after excision than on the first. The greater sluggishness of the colonic muscle was noticed also in pharmacological studies. Drugs which depressed the duodenum for thirty seconds often kept the colon paralyzed for five minutes or more. In some cases the drug caused a short drop and rise and then a permanent drop in the duodenum, but only the final drop in the colon. The contractions were very different, the rhythm irregular and the tone variable. The rate varied from 2 to 12 per minute. Unpublished experiments show also that the latent period of the colonic muscle is longer than that of the muscle in the small intestine. One cannot escape the impression that we have to deal in the small and large bowels with two very different types of muscle. The muscle in the colon acts more like the smooth muscle of a cold-blooded animal. The muscles in the small and large intestine, again, behave differently from the muscles in the body and antrum of the stomach.

Segments from sickly animals. The segments from sickly animals or animals heavily infected with parasites; generally beat poorly and irregularly. Sometimes they would begin beating well, or the first set would beat normally, but they generally became weak and erratic after a while. Sometimes segments from flabby looking intestines beat surprisingly well, with a very wide amplitude. The wide amplitude is probably a sign of poor tone (2). Ordinarily the duodenal and jejunal segments seemed to suffer most from the depression. Sometimes the duodenum would not beat at all even when the animal appeared to be pretty healthy. In some of the animals, short stretches of bowel were found to be flabby and filled with gas, while the rest of the gut appeared to be normal. It was interesting that when segments were excised from these peculiar regions they often failed to beat well, although the other segments behaved normally. Segments from rabbits whose abdomens were full of cysticerci generally beat well if the animal was well nourished and active. The colon did not seem to be much affected by the general depression and frequently it was the only segment that would contract normally. Segments of colon were markedly depressed in some animals with a tendency to diarrhoea. This agrees with x-ray studies in man which generally show the diarrhoeic colon unsegmented and flabby. The segments from the sickly animals often reacted poorly to drugs.

In one animal an inflamed Peyer's patch was noticed in the lower ileum. The inflamed segment, when excised and put into Locke's

solution, did not beat well and its rate was about normal. The segment just above, however, beat 21.5 to 25 times per minute. This

Fig. 3. Records from healthy and from diseased animals.

is not only twice the normal rate for the ileum but it is faster than normal for the duodenum. This shows what the writer has long sus

THE AMERICAN JOURNAL OF PHYSIOLOGY, VOL. 45, No. 4

pected, that inflammatory lesions can alter the gradients in the tract. These gradients may also be upset by the unevenness of the effects of disease toxins; that is, the duodenum and jejunum may be almost paralyzed while the ileum and colon remain active. Such a reversal was observed while studying the latent periods in different parts of the stomachs of distempered dogs (3). These observations may explain many of the digestive upsets in thin, run-down, nervous women; upsets for which no anatomical explanation can be found, but which straighten out promptly under over-feeding and rest.

Fig. 4. Ordinates represent rates per minute; abscissae represent the segments at varying distances from the pylorus. The solid line represents the average for fifty-three animals. The broken lines represent data from sickly animals.

Gradient of rhythm. The rate of contraction has been counted in one hundred and seventy-six places on records from fifty-three rabbits. These animals were in good condition and the segments contracted well. The averages are as follows: