Nathanson[11] discovered in the sea water the existence of bacteria which oxidize thiosulphate to sulphuric acid. They will develop if some Na₂S₂O₃, is added to sea water. These bacteria can only develop if CO₂ from the air is admitted or when carbonates are present. For these organisms the CO₂ cannot be replaced by glucose, urea, or other organic substances. Such bacteria must therefore possess the power of producing sugar and starch from CO₂ without the aid of chlorophyll. Similar observations were made by Beijerinck on a species of fresh-water bacteria.[12] [11] Nathanson, _Mitteil. d. zool. Station_, Neapel, 1902. [12] Beijerinck, M., _Folia Microbiologica_, 1914, iii., 91. Finally the case of iron bacteria may briefly be mentioned though Winogradsky’s views are not accepted by Molisch. We may, therefore, consider it an established fact that there are a number of organisms which could have lived on this planet at a time when only mineral constituents, such as phosphates, K, Mg, SO₄, CO₂, and O₂ besides NH₃, or SH₂, existed. This would lead us to consider it possible that the first organisms on this planet may have belonged to that world of micro-organisms which was discovered by Winogradsky. If we can conceive of this group of organisms as producing sugar, which in fact they do, they could have served as a basis for the development of other forms which require organic material for their development. In 1883 the small island of Krakatau was destroyed by the most violent volcanic eruption on record. A visit to the islands two months after the eruption showed that “the three islands were covered with pumice and layers of ash reaching on an average a thickness of thirty metres and frequently sixty metres.”[13] Of course all life on the islands was extinct. When Treub in 1886 first visited the island, he found that blue-green algæ were the first colonists on the pumice and on the exposed blocks of rock in the ravines on the mountain slopes. Investigations made during subsequent expeditions demonstrated the association of diatoms and bacteria. All of these were probably carried by the wind. The algæ referred to were according to Euler of the nostoc type. Nostoc does not require sugar, since it can produce that compound from the CO₂ of the air by the activity of its chlorophyll. This organism possesses also the power of assimilating the free nitrogen of the air. From these observations and because the _Nostocaceæ_ generally appear as the first settlers on sand the conclusion has been drawn that they or the group of _Schizophyceæ_ to which they belong formed the first settlers of our planet.[14] This conclusion is not quite safe since in the settlement of Krakatau as well as in the first colonizing of sand areas the nature of the first settler is determined chiefly by the carrying power of wind (or waves and birds). [13] Ernst, A., _The New Flora of the Volcanic Island of Krakatau_, Cambridge, 1908.