448 THE FUNCTIONS OF CROSS -STRIATED MUSCLES 



will produce the same amount of extension as a larg'e weight acting for a short 

 time. When a muscle has been extended greatly, its original length is recovered 

 by a single contraction and can be maintained for some time if several contrac- 

 tions follow one another. The activity of smooth muscles, therefore, is intimately 

 related to their elastic properties (P. Schultz). 



Smooth muscles cut out of the body immediately fall into a tonic state of 

 contraction, and exhibit in addition spontaneous rhythmical contractions. These 

 seem to be of purely muscular origin, for they appear in the rectractor penis 

 which has no ganglia, and have been observed as much as twenty-four hours after 

 the removal of the muscle from the body (Sertoli). They continue for an equal 

 length of time in the exsected frog's stomach (Woodsworth). In resting prepa- 

 rations they can be induced by a single mechanical stimulus, and also by appli- 

 cation of a constant current (Winkler). 



A simple contraction of a smooth muscle runs a very different course from 

 that of a skeletal muscle. The latent period is very long: in the musculature 

 of the frog's stomach one to ten seconds, in the retractor penis 0.8 second, in the 

 urinary bladder of the cat 0.25 second, and in the smooth muscles of the nicti- 

 tating membrane, after stimulation of the nerve, 0.3-0.5 second. With artificial 

 stimulation of the vasomotor nerve we get about the same value 0.3-0.5 sec- 

 ond for the latent period of the vascular muscles. The contraction reaches its 

 summit very slowly in the frog's stomach fifteen to twenty seconds, and then 

 falls still more slowly, sixty to eighty seconds. With the same muscle the 

 amount of shortening in a single contraction is forty-five per cent of its orig- 

 inal length, in tetanus fifty-nine per cent. 



Summation phenomena may be obtained if the stimuli follow one another 

 with sufficient rapidity; but they must not be identified with corresponding 

 processes in skeletal muscles. Here instead of a simultaneous contraction of 

 all of the muscular elements becoming stronger and stronger, we have to do 

 rather with repeated contractions of the different cells in varying sequence 

 (Zilwa, Schultz). 



Finally, inhibition of tonic contractions can be demonstrated on smooth 

 muscles. The tonus of the retractor penis can be intercepted by means of the 

 constant current (Sertoli), and corresponding phenomena have been obtained 

 in the frog's stomach. Furthermore, we know that the smooth musculature of 

 the blood vessels and of the intestinal wall are under the influence of inhibi- 

 tory nerves. 



SECOND SECTION 



RECIPROCAL RELATIONS BETWEEN THE MUSCLES AND 

 OTHER ORGANS OF THE BODY 



In the performance of their functions the muscles influence, and in many 

 ways are influenced by, the other organs of the body. A muscle degenerates 

 if its connection with the central nervous system be interrupted, and within 

 a relatively short time it becomes transformed into a mass of connective tissue. 

 The same thing happens if the motor cells in the anterior horn of the spinal 

 cord be destroyed by a lesion. The cause of degeneration under these circum- 

 stances is not that the muscle is inactive. Inactivity, as it appears, for ex- 

 ample, as the result of brain disease, involves a reduction of the muscle 

 substance, an atrophy, but the muscle does not degenerate; it retains its 



