Abstract
Sherrington 1 has summarized rather completely our knowledge of tonus for smooth and striated muscle. He believes that muscle fiber is not to be considered as an elastic string, for it has the property of exhibiting different lengths with one and the same degree of tension. This doctrine is of special interest in the case of the abdominal musculature, which is of necessity subject to many changes in pressure due to the many variations which occur in the abdominal contents. We should therefore expect to find the muscle fibers of the abdomen showing different lengths with the same degree of tension, or, to put it conversely, to exhibit a fairly constant pressure with varying increments of volume.
The object of these experiments has been to determine whether this regulation of inter-abdominal pressure is essentially a function of the nervous mechanism of the abdominal walls or of the intrinsic musculature itself.
Cats were used in these experiments under the several conditions of light and deep anesthesia and decerebration. A cannula introduced into the abdominal cavity was connected by a 3-way stopcock with a manometer and a burette filled with 0.9 per cent. sodium chloride solution kept at a temperature of 38 degrees centigrade. Costal respiration was recorded throughout the experiment. The warmed saline was admitted to the abdominal cavity at the rate of 10 C.C. a minute. With each increment of fluid the pressure was read from the manometer and plotted against the volume. A curve was thus obtained for the entire experiment, which, in about fifty cases was found to be typical. There was a slow increase of pressure in proportion to volume until a certain point was reached, from which pressure rose much more rapidly.
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