Experimental observations on the functional significance of the sympathetic innervation of voluntary muscles.

In this study we adopted the plan of extirpating the sympathetic trunk in the lumbar region on one side only, using dogs as the experimental animals, and comparing the tonus, the power of contraction and the resistance to fatigue of the muscles of both hind limbs both immediately after the operation (6 dogs) and after ample time (10 to 36 days) had been allowed for the degeneration of the sympathetic nerve-fibers supplying the muscles of the hind limb on the side of the operation (4 dogs). 1 Only the more important results obtained can be reported in this paper.

In the animals which were allowed to live following the operation a degree of hypotonus of the muscles of the hind limb on the side of the operation could be demonstrated by palpation for some time, but gradually subsided. This is in accord with the observations of Negrin, Lopez and von Brücke (1917) 2 and Dusser de Barenne (1917) 3 on cats. We are not prepared to state how long such hypotonus persists. In one animal it was still demonstrable two weeks after operation, in another it could not be demonstrated by palpation ten days after operation. However, when these dogs were placed under surgical anesthesia, even after the hypotonus referred to had apparently subsided, a marked difference in the flaccidity of the muscles of the two hind limbs became apparent. As the animals lay on their backs with the limbs free the hind limb on the side of the operation dropped to a lower position than the other. When equal weights of 100 or 200 grams were attached to both hind feet and suspended over pulleys at the end of the table the limb on the side of the operation was more fully extended than the other. Weights of 600 grams drew both limbs out equally, both being fully extended.

In order to secure graphic records of the contractions of individual muscles the hind limbs were fixed in moderate extension, as the animal lay on its back under surgical anesthesia. The tendons of the gastrocnemius muscles were isolated and cut at their insertions. A strong cord was attached to each isolated tendon and led over a pully at the end of the table to an ergograph or to a muscle lever with a weight attached. The sfimulating current was supplied by two or three dry cells and an inductorium. The stimulus was applied to the exposed sciatic nerves.