Cold applied to the head, while hot mustard-water is used to the feet, is one of the simplest modes of equalizing the cerebral circulation. It must, however, be used with caution where cerebral anaemia is readily induced, as in weakly subjects. Ice to the nape of the neck also acts well, and sometimes the alternate use of cold and hot applications gives the best results. This is especially the case in the congestion of opium-narcosis, uraemia, and carbonic acid poisoning (Bar-tholow).