Abdominal Musculature in Cat. 145 



78 (1538) 



The effect of varying pressures upon the abdominal musculature 



in the cat. 



By Helen C. Coombs. 



[From the Department of Physiology, Columbia University.] 



Sherrington 1 has summarized rather completely our know- 

 ledge 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 condi- 

 tions 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. 

 At this point also, costal respiration increased very greatly in 

 depth to effect a compensation for the lack of adequate abdominal 



1 Sherrington, Brain, 1915, xxxviii, 191. 



