Our examination of phosphorus and sulphur from the functional point of view throws light also on their effect on the alternating conditions of waking and sleeping, necessary for the life of the higher organisms. This rhythmic change, which affects especially the nervous system, is an alternation between the qualities dry and moist. Disturbance of this alternation in one direction or the other makes it difficult for the organism to react in full wakefulness or normal sleep. It follows that treatment with phosphorus or sulphur in suitable preparations, according to the nature of the disturbance, can be beneficial. If we study the functional properties of such substances we see that they can teach us a rational understanding of therapeutic practices, which otherwise must remain mere results of trial and error. The same applies to phosphorus and sulphur treatment in cases where in the functionally 'dry' bone system or in the functionally 'moist' metabolic system of the organism the wrong quality predominates. If the bones remain too 'moist' there is a tendency to rickets; against this, certain fish-oils are a well-known remedy on account of their highly phosphoric nature. Conversely, the application of sulphur can help where weakness of the metabolic forces produces rheumatic or gouty sediments in parts of the body whose function is to serve by their mobility the activities of the will. In this case the abnormal predominance of the quality 'dry' can be counteracted by the medical application of sulphur. * Having observed the action of sulphur and phosphorus in the laboratory and in living organisms, we will now turn to phenomena of a macrotelluric nature which reveal the participation of sulphur and phosphorus. There, sulphur points unmistakably to the earth's volcanism. It is a fact that, wherever mineral sulphur occurs in the earth, there we find a spot of former or present volcanic activity. Similarly, there is no such spot on the earth without sulphur being present in one form or another. Hence the name Solfatara for the fumarole described in Chapter IX. Once again it is the Solfatara which offers us a phenomenon, this time in connexion with the special role sulphur plays in its activities, which, regarded with the eye of the spirit, assumes the significance of an instance 'worth a thousand'. In spite of the very high temperature of the sulphurous fumes emitted from various crevices on the edge of the Solfatara, it is possible, thanks to the complete dryness of the fumes, to crawl a little way into the interior of these crevices. Not far away from the opening of the crevice, where the hot fumes touch the cooler rock surface, one is met by a very beautiful spectacle - namely, the continual forming, out of nothing as it seems, of glittering yellow sulphur crystals, suspended in delicate chains from the ceiling.