IV. The automatic action of the sphincter ani

Abstract

The observations described in the following paper had for their object the determination of the form of the reflex or automatic action of the sphincter ani of man when voluntary power over it is lost. This reflex action is believed, from the researches of Masius, to depend on an “ano-spinal centre,” situated in the lumbar enlargement of the spinal cord, controlled in health by higher (encephalic) centres. It appears, however, to be very uniform in its character in various conditions, the most conspicuous common character of which is the entire loss of voluntary power. The larger number of observations were made on a man who, by a violent fall on the sacrum, had apparently injured the posterior roots of all the sacral nerves and both roots of the lowest sacral nerves. A de­pression existed over the lower part of the sacrum. Sensibility to touch and pain was lost in all parts supplied by branches from the sacral plexus, the limitation being exact. There was no muscular paralysis or loss of nutrition except in the levator ani, the sphincter ani, and the sphincter vesicse, all of which were paralyzed to the will. The anus and the mucous membrane of the rectum were quite insensitive. There was no evidence of any injury to the spinal cord; with this, indeed, the symptoms were incompatible. It would thus appear that the only lesion was a division of the direct communication between the sphincter and the cord. Other observations were made on two patients with para­plegia, due probably to disease of the dorsal region of the spinal cord, in whom there was reason to believe that the lumbar enlargement of the cord was free from material damage. In each case there was not the slightest voluntary power to retain the contents of the rectum. It was found that in each the condition of the sphincter was essentially the same, and that it was in a state of high reflex activity. The most uniform results were obtained in the case of injury to the sacral nerves. Finally these results were compared with those obtained by the same method when voluntary power was intact.