ANIMAL MECHANICS. 



163 



force of the abdominal muscles, I placed two men, of 48 and 

 2 1 years of age, respectively, lying on a table upon their backs, 

 and put a disk measuring 1.87 in. diameter just over the 

 navel ; weights were placed upon this disk, and gradually in- 

 creased until the extreme limit of weight that could be lifted 

 with safety was reached ; this limit was found to be, in both 

 cases, 113 lbs. As the circle whose diameter is 1.87 in. has 

 an area of 2.937 sc l uare inches, the pressure perpendicular to 

 the abdominal wall produced by the action of the abdominal 

 muscles is, 



1 1 3 



P= — = 38.47 lbs. per sq. inch. 



2.937 



The force is somewhat greater than that calculated from this 

 curvature of the belly, and the coefficient of muscular con- 

 traction, already determined; viz. 32.93 lbs. per square inch. 

 It should be remembered, however, that in my experiments 

 on the abdominal muscles, I pushed the trial of strength al- 

 most to the verge of producing slight peritonitis, as both the 

 subjects of my experiment complained of sharp shooting 

 pains in the abdominal walls for 24 hours after the experi- 

 ments were made. 



The foregoing theory of the muscular forces employed in 

 parturition leads us naturally to be cautious in the use of 

 chloroform, and other ana3sthetics, which produce their effects, 

 first upon the voluntary, and afterwards upon the involuntary 

 muscles. When chloroform is used, in parturition, beyond 

 the stage at which it produces simple drunkenness, and indif- 

 ference to pain, it is positively injurious; for it destroys the 

 action of the voluntary abdominal muscles, which constitute 

 the chief part of the force employed in difficult labours. 

 Hence, the muscular tissue of the uterus is left to overcome 

 an obstacle beyond its strength, and without the aid that na- 

 ture intended to be given by the abdominal muscles. The 



