From what has already been said, it is apparent that changes in respiration and blood pressure may be produced by stimulation of a very large portion of the optic thalamus; that no one region controls these phenomena; that the spleen shows variations in volume only when marked blood pressure changes occur, and that such a change has been observed on stimulation of many places in the thalamus. Furthermore, the regions in the thalamus from which such effects are obtained are those in which the large afferent paths end; namely, the fillet and superior cerebellar peduncle, and a region directly connected with the vagus nucleus. The portions of the thalamus which proved inert to stimulation were those which in our previous investigation also were inactive; namely, the median nucleus, and the upper anterior end of the lateral—the region through which the fibers of the median nucleus pass.
These phenomena are similar in every respect to those observed when an afferent nerve is stimulated. In what has gone before, it has been shown that the respiratory and circulatory changes occurred when one of the sensory paths, or a path running directly to the medullary nuclei governing these functions was stimulated. In explaining these phenomena, therefore, there is no necessity for invoking the existence of special centers.