The innervation of the frog's heart. I. An examination of the autonomic postganglionic nerve fibres and a comparison of autonomic and sensory ganglion cells.

The pa tte rn of innervation in the frog’s heart shown by silver staining has been compared w ith the results of histochemical methods. The muscle innervation is a series of dense n e t­ works of nerve bundles. These have been divided into four groups according to their size and distribution. The silver m ethods show fewer fibres than the histochemical methods bu t all the methods show the same distribution of fibres. The ganglion cells in the vagal, dorsal root and sym pathetic ganglia, and in the vagosym pathetic trunks and heart, have been examined w ith silver staining and histochemical methods. I t has been concluded th a t the vagal ganglion cells are probably sensory; th a t the sym pathetic ganglion cells are confined to the sym pathetic chain; and th a t all the cells in the vagosym pathetic trunks and heart are parasym pathetic m otor cells. Section of the vagosym pathetic trunks causes loss of all fluorescent nerve fibres from the heart, while a t the same tim e there are no changes in the distribution of acetylcholinesterase-containing fibres in the muscle. I t is concluded th a t the fluorescence and acetylcholinesterase methods show respectively the sym pathetic and parasym pathetic postganglionic fibres. There is no evidence from this work to support the claims th a t some recently described and extensive plexuses of fibres on the muscle are in fact nervous in origin.